“That’s huge,” said Kathy Hirsh-Pasek, a professor of psychology at Temple University in Philadelphia, who was not involved in the survey, which was published in the journal Pediatrics. “If children are sitting by themselves glued to digital candy, we simply don’t know what the consequences are for their early social development.”

In the survey, 350 parents, who were largely African-American, filled out a questionnaire while visiting Einstein Medical Center in Philadelphia.

One-third of the parents of 3- and 4-year-olds said their children liked to use more than one device at the same time, noted Dr. Hilda Kabali, a pediatrician and the lead author of the survey.

Seventy percent of the parents reported allowing their children, ages 6 months to 4 years old, to play with mobile devices while the parents did housework, and 65 percent said they had done so to placate a child in public.