BOURNE — Mason Anderson’s short life has rarely been as serene as it was one recent afternoon, when the 2-year-old slept soundly for a few hours, bundled in a soft red blanket decorated with tiny hearts.

His grandmother, Susan Lopes, looked at the usually hyperactive child with a weary half-smile. “I love Mason. I love him being in my life,’’ she said before breaking down in tears.

Mason was born dependent on heroin, the child of Lopes’s drug-addicted son and a woman who overdosed just three days later while her baby struggled in the hospital.

The child’s mother survived. But his father, Justin Anderson, died of a heroin and fentanyl overdose in November. The next day would have been his 29th birthday, which Lopes planned to celebrate with lasagna and a birthday cake.

Now, Lopes is struggling to raise a little boy orphaned by the opioid epidemic raging across Massachusetts, where thousands of children of drug-dependent parents have been placed in state custody or are being raised by grandparents and other relatives.

The sprawling drug crisis, which public health officials have described as the worst in American history, has touched nearly every part of society. But the burden has perhaps fallen hardest on children, creating a new generation of foster youth and placing extraordinary strain on the child welfare system.

Since 2013, the average number of children and young adults in state custody has risen 26 percent to more than 9,200 in August, according to the Department of Children and Families, the state’s child protection agency.

Petitions to remove children from their homes rose 57 percent statewide from fiscal 2012 to fiscal 2016, rising from 2,460 to 3,855 before declining 10 percent this year. Reports of babies born with opioids in their systems rose 11 percent from fiscal 2015 to fiscal 2017, to 2,675 from 2,393, according to DCF figures.

The increases have coincided with the spread of the opioid epidemic. As a result, said Maria Mossaides, head of the state’s Office of the Child Advocate, the reasons for removing children from their parents’ homes have changed dramatically. “You’re seeing a huge increase in allegations of neglect or abuse with respect to parents who are users of drugs,’’ she said.

The plight of these children, some of whom have seen their parents dead from an overdose, has overwhelmed a system not intended to handle such heavy demand. The influx of children has created a shortage of foster parents, saddled social workers with daunting caseloads, and placed enormous pressure on the juvenile court system, which decides whether a child should be placed in state care.

“These are very complex cases. We know that even one day in alternative care for a child is very traumatic,’’ said Amy L. Nechtem, chief justice of the state Juvenile Court. “We know that many, many are opioid-related.’’

Despite the new challenges, DCF Commissioner Linda Spears said the agency has made important strides since the death of 5-year-old Jeremiah Oliver in 2014 exposed startling lapses in its oversight of at-risk children. The murder the following year of Bella Bond, a 2-year-old whose body was discovered in a trash bag, underscored the dangers that children face from opioid addiction in the home.

“Each and every day, we place each and every kid that needs to be placed,’’ said Spears, whose predecessor resigned after Oliver’s body was discovered stuffed in a suitcase off Interstate 190. A DCF social worker had missed eight mandatory monthly meetings with the Fitchburg boy in a span that overlapped his disappearance.

Part of the strain on DCF can be traced to those highly publicized deaths, child advocates said. In their aftermath, social workers became more likely to take a child into custody rather than risk an unforeseen tragedy.

At the same time, the rapid growth of the opioid epidemic added another enormous obstacle as the department worked to reform its culture and protocols.

“The work that the department is currently doing in revamping policies and upgrading systems . . . all happened coincidentally with this huge rise in numbers,’’ Mossaides said.

In the past two years, the department has increased its staff of social workers by 300, Spears said. About 140 new foster homes have been added, and 15 new recruiters are working to increase that number. Most important, caseloads are shrinking, the commissioner said.

As of July 31, the average “weighted caseload’’ for DCF social workers was 18.7, according to state data, only slightly above the contracted target of 18.0. That figure, which measures the complexity of cases as well as overall numbers for rank-and-file social workers, represents a marked improvement from past years, officials said.

“There’s enough work going on and enough expansion going on that I don’t see us as being in a crisis,’’ Spears said.

But Peter MacKinnon, president of the union that represents DCF social workers, said caseloads remain at dangerously high levels in parts of the state, and that some children who should be removed from their homes might slip through the cracks.

“You end up triaging, and you make decisions that you hope are the right decisions, and there is no way to predict that,’’ he said. “Opioid cases are incredibly difficult to deal with because the risk to children can be so great and so high.’’

DCF does not count how many reports of child abuse and neglect are related specifically to opioids. Instead, the department includes those cases with other forms of substance abuse, such as alcohol. As a whole, substance abuse has been linked to 28 percent of child abuse and neglect allegations since March 2016, the most frequent reason cited.

Domestic violence is next at 21 percent, followed by mental illness at 11 percent.

DCF officials said some positive signs have emerged in the past year. Child-removal petitions have dropped and the number of children in state custody has stabilized, dipping to 9,517 in March from 9,655 in June 2016.

“What I think we’ve done clearly is stem the growth, and that’s a positive sign to me,’’ Spears said.

Governor Charlie Baker has said child-welfare reform is a priority of his administration. Lizzy Guyton, a spokeswoman for Baker, cited more than $100 million that has been invested to bolster DCF, which has doubled its number of substance-abuse coordinators and joined a state task force to coordinate services for opioid-exposed newborns.

Erin Bradley, executive director of the Children’s League of Massachusetts, praised the state’s efforts.

“The commissioner and the Baker administration really have done yeomen’s work in shoring up the foundation of the Department of Children and Families,’’ Bradley said. As an example, she cited policy changes to streamline how families are assessed and monitored.

Yet many child advocates and state officials predict a difficult, drawn-out campaign to protect children traumatized by opioid addiction. To Nechtem, the juvenile court’s chief justice, one year of encouraging data does not constitute a trend.

“These are some of the most heart-wrenching cases, but I also feel they’re some of the most heart-warming cases,’’ Nechtem said. “The laser focus is on the best interest of that child.’’

Bradley cautioned that the epidemic’s long-term impact will not be apparent until today’s children become adults. John Merrigan, register of Probate and Family Court in hard-hit Franklin County, said the struggle could last generations. In response, government agencies and treatment providers must join forces to help those with addiction and their children, he said.

“Every person needs to take a responsible role in fighting this and coming together,’’ Merrigan said. “If not, we’re just going to continue butting our heads against a wall and watch people die.’’

The opioid crisis has hit children particularly hard on Cape Cod and the Islands, where court petitions to remove them from troubled homes nearly doubled between 2012 and 2016. Petitions have dropped 14 percent since then, but child welfare specialists remain wary.

“It’s encouraging to see a decrease in filings fairly uniformly around the state, but it’s too soon to say if it’s a trend that will continue or what it means,’’ said Susan Elsen, child welfare reform project director at the Massachusetts Law Reform Institute, a nonprofit poverty law and policy center.

At the DCF’s Hyannis office, an average of about 19 families were assigned to each of the 52 social workers with ongoing cases at the end of July, the highest rate in Massachusetts, according to union representatives. Their contract with the state stipulates that social workers be assigned no more than 15 families.

“If you have too many people that you’re required to talk to on a monthly basis, you’re not digging in to ask the questions that need to be asked, simply because you don’t have the time,’’ MacKinnon said.

The union steward in Hyannis described a crushing caseload for many social workers, who often stay with DCF for only one or two years before leaving. At the end of July, nearly half of DCF social workers for Cape Cod and the Islands were handling more complicated cases than nearly all of their colleagues across the state, according to the union.

“They come on board and they’re raring to go, and they want to do this work, but it becomes so difficult to explain the stress of it. It becomes a little demoralizing,’’ said Mary Burkinshaw, the union steward.

“A lot of these children have been exposed to trauma," added Burkinshaw, who also supervises a small group of social workers. “They have seen or experienced their parents overdosing. Some have found a parent or important adult in their life dead from an overdose.’’

Protecting those children forces social workers to take extraordinary measures, Burkinshaw said. As many as 10 children sometimes spend the day in the Hyannis office, waiting for the agency to find a bed that can be more than 50 miles away, she said.

“We’re really not equipped to be a day care,’’ Burkinshaw said.

Social workers sometimes drive a child to a faraway foster home after their shift, catch a few hours sleep, and then return to the home as early as 5 a.m. to pick up the child. Along the way, social workers have been bitten, spit at, and punched while driving, Burkinshaw said.

“The children we’re seeing are more traumatized than the kids I saw when I was a worker,’’ Burkinshaw said. “Most of the cases that are coming in now are substance-abuse related, and most of them are linked to opioids.’’

Lopes is among an estimated 10,000 grandparents in Massachusetts who are primary caregivers for their grandchildren, many of whom can no longer live safely with drug-dependent parents.

Now, at 54 years old, Lopes is raising a rambunctious toddler who does not know his mother. “It’s emotionally and physically exhausting. You’re running on empty,’’ Lopes said.

Brightly colored toys — a helicopter here, a police cruiser there — take up much of the living room of her two-story home near the Cape Cod Canal. Mason is playing happily, but Lopes knows this is only a short break in another demanding day.

Weaned from heroin as a newborn, Mason rarely sleeps through the night. He cannot put more than one or two words together, and he is prone to outbursts.

Lopes, who plans to file for adoption, is learning as she goes. She lost her son to opioids, and now she is determined to save her grandson.

“This will be my life until my last breath,’’ Lopes said. “He’s who I live for.’’

Brian MacQuarrie can be reached at brian.macquarrie@globe.com.