Car free neighbourhood streets
The biggest deterent keeping children from playing with their neighbours outside is traffic on streets. If streets didn't have so much traffic, parents would let their kids roam around, giving them greater freedom and independence. We need to design neighbourhoods for kids, not cars. Cities can identify already car quiet streets and block small parts off so kids can congregate and play. Phase two would be identifying places where traffic could be rerouted to increase this pedestrian/play friendly space and phase three would be to regulate all future development to plan spaces for children playing together, not cars getting from point A to B.