In families which own tablet computers, almost a third of children aged under five have their own device, according to a study by the universities of Sheffield and Edinburgh.
Children use their computers for more than an hour a day, researchers say.
The study showed YouTube was the most popular destination.
Jackie Marsh of the University of Sheffield said parents needed to check the appropriateness of what their infant children were using online.
The study revealed the widespread use of tablet computers among toddlers, averaging an hour and 19 minutes on weekdays and slightly longer at weekends.
You can read the full report from the BBC at Tablet Computers Widely Used by Under Fives.