A child can switch from a cartoon to a game to a short video in seconds. That speed is part of what makes screens so appealing, and part of why many parents wonder what all that stimulation is doing to a growing brain.

Parents often hear that screen time is either harmless or harmful. The evidence is more nuanced: what children watch, when they watch, what screens replace, and whether an adult is involved all matter. Here is a practical, science-informed guide to the current research.