You touched on exercise, more as an alternative to 'caravans of private cars', but I would like to elaborate a touch.
As much as climate change (or man's affect of) is supposedly the biggest threat to the planet, the biggest threat to man is obesity. You mentioned a couple of things that the kids are doing wrong, but I'd suggest the kids are getting the food and laziness habits from us oldies
I'm involved with kids sport, and with these smaller families that we are having, in many cases kids don't have a brother or sister to kick or throw a ball with. The result seems to be a lot more uncoordinated kids when they begin sport, and most parents treat their child's sport as a form of cheap babysitting, so don't help develop their sporting choices. You mentioned 'electric devices', which we had to ban the kids using during training, as they'd be on them the whole time, instead of being involved in the activity they were there for.
Anyways, just a little slight digression on your very clever opening post.