The study found that children who have more than two hours of screen time a day got lower scores on tests focused on thinking and language skills.

….These negative effects occur because children don’t know how to translate two-dimensional skills learned on a screen to the real, three-dimensional world. “If you give a child an app where they play with ..,virtual blocks, and stack them, and then put real blocks in front of them, they start all over.” 

Over 2 hours of screen time a day can affect children’s brains, study finds – INSIDER

hmmm