As Charina Santos’s son, Jace, approached his first birthday, he was making eye contact, waving and starting to feed himself — the usual developmental milestones that pediatricians track. Then, within a couple of months, he stopped. “I would try to get him to engage, but it just wasn’t there,” Ms. Santos said. Soon after, Jace was diagnosed with autism.

About six months later, Ms. Santos gave birth to a daughter, Juliette. Shortly before Juliette turned 1, the same thing happened: She began to lose developmental skills and was soon diagnosed with autism.

Ms. Santos, a single mother, was overwhelmed. Jace would run away whenever they went outside, and Juliette had trouble walking. They couldn’t go to the playground or take the subway. Staying home was difficult, too: Children with autism are often sensitive to noise, light and touch, and the children could hardly be in the same room together without setting off a meltdown. For a family that lived in a one-bedroom apartment in the Bronx, that presented a problem. “It was just very isolating,” said Ms. Santos.

Ms. Santos wasn’t sure if she could find child care, much less afford it. The federal government requires school districts to provide special education services starting at age 3, but New York, like most states, has failed to meet that requirement. As a result, many children who need such services in New York are left without adequate care. The alternatives are prohibitively expensive: Ms. Santos would have paid about $3,250 per month at the market rate.

A turning point came when Ms. Santos learned about the Kennedy Children’s Center, which offers free, full-day preschool for children with developmental delays in the Bronx and East Harlem. Its programs are supported by Catholic Charities of New York, one of the original beneficiaries of The New York Times Communities Fund.

Ms. Santos enrolled Jace, and later, Juliette, in the center. In each classroom, six to 12 children are paired with one teacher and two teacher’s aides. The children also work with specialized therapists to help them speak, walk and gain skills like holding a pencil or putting on a coat. Outside, the children climb on the playgrounds, tend to the garden and ride tricycles.

Within months, Ms. Santos saw her children change. Jace now loves music and dancing. A few friends recently joined him to celebrate his sixth birthday with a party, something that once seemed impossible. Juliette has learned not only to walk, but to run, jump and dance. She comes home from the center singing and hugging her brother, who sometimes even returns her embrace.

For her part, Ms. Santos joined a parent support group and workshops at the center, which have helped her adopt new parenting tools and feel less alone. “We found home,” said Ms. Santos.