Mr. de Oliveira, 21, resumed paying child support, and increased the amount. Ms. Vieira now allows him to see Daniel.

“I still pray to God so that he can be a healthy and perfect child,” he said. “I keep asking, keep asking, keep asking.”

The afternoon after the medication crisis, Ms. Vieira, sifting among pregnancy ultrasounds showing Daniel’s underdeveloped head, found a photo of him smiling. “I love this smile,” she said. Because of Daniel, “I am a better human being,” she said, adding that “if I had had a normal baby, I would not have given as much attention.”

She worries about being inattentive to her 5-year-old, João Pedro. Even while walking him home from school, she carries Daniel, shielding him from sun with a turquoise umbrella. One day, João Pedro playfully covered Daniel’s face with his hand, chanting, “Are you smiling?” When Daniel didn’t respond, João Pedro scampered to a rusty playground, near weathered horses nibbling meager grass.

Later, when his neurologist, Dr. Maria Durce Costa Gomes Carvalho, squeezed Daniel into her packed schedule, his rare smile was still absent. He cried and cried. “Look at this tantrum, Daniel, oh my God!” Dr. Gomes exclaimed.

“He did not used to be like this,” Ms. Vieira said.

Dr. Gomes asked if Daniel looked at things.

“Not a lot,” Ms. Vieira said.

“Even with glasses?”

“No.”

Daniel’s medication was adjusted, reducing his seizures. Dr. Gomes couldn’t predict if he would walk or talk. “What matters — right, Jaqueline? — is their every achievement.”