On Monday afternoon, the convergence of mothers and strollers and babies on the second floor of the office building on Franklin Street downtown began to resemble southbound traffic coming out of the Tip O’Neill Tunnel at rush hour.

Max Julien sat there at the main desk, answering a phone that wouldn’t stop ringing.

“It’s busy,’’ she said. “But you know what? There are some people who have come before but won’t come now. They’re afraid.’’

Afraid of Christmas? Sad.

The essence of Christmas was unfolding in the area of the Kennedy Brothers Physical Therapy clinic that is reserved for mothers — and it’s almost always mothers — signing their kids up for Christmas in the City.

Founded by the irrepressible Jake and Sparky Kennedy, Christmas in the City began in 1989 with 165 homeless kids. On Sunday, they’re expecting 6,000 kids at the Boston Convention & Exhibition Center.

Just stop and think about that: There are at least 6,000 homeless kids within an hour’s bus ride of Boston this Christmas. Jesus would weep.

“This will be the most kids ever,’’ Jake Kennedy was saying, in between working out his patients, who did their therapy amid training tables, exercise equipment, and boxes of toys that conjured images of what Santa’s workshop would look like if it had a PT clinic inside.

“The need grows, every year,’’ he said. “We never have enough toys.’’

On Monday, the day after the big gig, volunteers will hand out additional toys and clothing to 16,000 kids who, while not technically homeless, are poor and whose families don’t have the money to spend on gifts.

But even as the need grows, the volunteer army that turns out every year noticed a difference this year.

“We just had a woman in here,’’ Max Julien was saying. “She had a friend who is too afraid to come here and sign her kids up because she’s undocumented. She’s not alone. There are others.’’

The fear among some of these mothers is, if immigration agents would go to hospitals, schools, and churches to arrest undocumented immigrants, what’s to stop them from raiding Christmas in the City?

Welcome to America, 2017. Again, ­Jesus would weep.

But most people are decent. And so the call goes out, every year, in the run up to the transformation of the Convention Center into a winter wonderland with amusement rides and costumed performers and more Santas than the Mall of America.

Christmas in the City began with the simple but profound concept that every child, even a poor child without a home, should be able to open the one gift they wanted most for Christmas. You can go to christmasinthecity.org, call Kennedy Brothers at 617-542-6611, or stop by the downtown clinic at 45 Franklin St. to contribute a gift or get the name and wish list of a homeless child.

You can do the same at any of the Kennedy Brothers clinics in Cohasset, Braintree, Needham, and Watertown. You can drop toys off at Lexington Toyota or the Seaport Hotel, where you can valet your car for free.

This year, for the first time, they are going to open the winter wonderland at the Convention Center on Saturday, a day before the event.

“We’re hoping to start a new tradition, so that people of means can bring their kids to see what Christmas in the City is all about,’’ Jake Kennedy said. “You can bring your kids in, let them go on the rides, and hopefully bring a present and leave it with us so we can give to the kids coming the next day or the day after.’’

Jake Kennedy believes the gifts go both ways. “Your kids will see the difference between the haves and the haves not and create that empathy we need now, more than ever,’’ he said.

It’s also an opportunity, actually a gift, to remember that the family that celebrated the very first Christmas did so in a stable, because they didn’t have any other place to stay.

Kevin Cullen is a Globe columnist. He can be reached at cullen@globe.com