George Carlin summed this up pretty well - "When does a kid get to sit in a yard with a stick anymore? You know, just sit there with a fucking stick. Do today's kids even know what a stick is?" - https://www.youtube.com/watch?v=K0MKBdD2FGA
We try to make sure we carve out time for them to strategically be bored. Forced to explore, use their imaginations, build a fort, stomp on bugs, make shit up.