Don’t listen to one anecdotal opinion and conclude it’s a US problem. My neighbors kids are outside almost everyday after school and I know of others who have sports practice and other daily activities that aren’t spent inside.

The main difference between US and Europe is the way the cities are setup. Much more walkable and urban centric in EU. Populations are much denser. It was a nice change of pace to be able to walk everywhere last year when I was in Italy.