Kids from my neighbourhood consistently come and knock on our door to play with our kids outside (and vice-versa) - not from the States, Canada. Even if there are no other kids to play with I send mine outside to play in the yard, that's how they met most of the kids in the neighbourhood to begin with.
We (my neighbors and I) had to institute a rule that if the gate is shut no knocking on our door because all the kids were running around knocking on each others doors so much. No one could get a meal in or sleep in on the weekend past 8.