Early childhood education providers are furious after the state announced a new coronavirus testing program last week for public schools without including day-care centers and after-school programs, which are still struggling to serve more than 100,000 children almost a year into the pandemic.

On Monday, more than 250 early education and out-of-school providers, advocates, and associations sent a letter to Governor Charlie Baker urging him to include their industry in the testing program.

“Clearly, we are not essential enough to benefit from the same health and safety measures meant to protect the lives and wellbeing of our K-12 brothers and sisters who care for the same families that we do,’’ the letter read.

Many of these centers have stayed open since the summer, transforming into impromptu schoolhouses this fall when many districts turned to remote, virtual learning. The workers — many of them women and people of color — have been on the front lines as they care for the children of other frontline workers, yet the centers have been left largely to fend for themselves. They have bought their own protective equipment and extra cleaning supplies, and found creative ways to test workers who might be sick.

“The Commonwealth cannot continue to deny early education and care and afterschool staff, students, and families the critical health and safety supports provided to K-12 schools,’’ the letter said.

After months of urging from teachers unions, superintendents, school committees, and public health experts, Baker announced a program that will offer voluntary testing to any school district that has in-person classes. The program aims to allow more students to return to the classroom. It will be free for the first six weeks, and students and staff can decline to participate.

The Baker administration said Monday the small size and varied attendance of many child- care programs makes widescale testing “a difficult strategy to employ.’’

“The Department of Early Education and Care continues to prioritize and support restoring and maintaining quality child care for the more than 6,000 licensed early education providers across the Commonwealth that are currently open and caring for children,’’ said state spokeswoman Colleen Quinn.

More than 400 centers have closed since the beginning of the pandemic in Massachusetts but those that have managed to stay in business are struggling.

The centers serve children of all socioeconomic groups but they are particularly vital to low-income parents, many of whom do not have the luxury of working from home.

Attendance at these centers during the pandemic has been highest in the 11 cities and towns that have the highest risk of COVID-19, according to the state.

Early education workers say the Baker administration left out a particularly vulnerable set of frontline employees.

The early education workforce is 92 percent female, and 32 percent people of color, according to information from the state Department of Early Education and Care. Workers speak more than 24 primary languages.

And more than 80 percent of early education providers in the state are minority- and women-owned businesses.

In Massachusetts, they earn an average of $30,090, or 34 percent less than public school preschool teachers, according to state data. One in five are the sole earner for their family and nearly half support other family members.

Many early education providers said their exclusion from the testing program is an example of how the sector has been historically overlooked and underfunded.

But because this latest oversight comes amid a deadly pandemic, providers say it is now a matter of life and death.

“It is a question of honoring the dignity and the humanity of those who are in this field, treating them equitably and fairly,’’ said Renee Boynton-Jarrett, a pediatrician at Boston Medical Center who signed the letter sent to Baker.

“It’s also a question of the degree to which we are investing in children and the next generation, and the factors that contribute to them thriving,’’ added Boynton-Jarrett, who is also a social epidemiologist and assistant professor of pediatrics at Boston University.

Also among the letter’s signatories was the Boys & Girls Clubs of Dorchester, which, like many centers, reopened in person as soon as it was allowed in July.

In addition to their regular after-school and day-care services, the center now serves about 130 students who come daily from 7:30 a.m. to 5 p.m. to do virtual schooling while their parents work. Staff help them with their studies and also provide meals and other types of enrichment like music and art.

“They’re not in school, they’re here,’’ said Mary Kinsella Scannell, senior vice president of education and programming at the club.

“Testing being available is really important. It will help keep our programs open and it will help keep our children and staff safe,’’ she said.

In the absence of any testing system for early education centers, one organization, Neighborhood Villages, set up its own pilot program for eight child-care centers. The initiative, which is privately funded, has tested about 530 staff on a weekly basis since late November. The program uses a saliva test that is self-administered. No nurse is required and no personal information is shared with the lab.

Lauren Kennedy, cofounder of the early education advocacy organization, said their model could be scaled up if the state invested in it.

“Ultimately it is a statement of whose lives we value and whose we do not,’’ she said.

Laura Krantz can be reached at laura.krantz@globe.com. Follow her on Twitter @laurakrantz.