would you let your kids go inside neighbor's house without you?

[Anonymous]

This is why I pay people to watch my kids.

[Anonymous]

I let my kids play at neighbors' houses whom I don't know well, my mom lets my kids play neighbor's house whom I don't know at all.

You should get to know these neighbors. Worst case: you find you don't trust them and have an actual basis to ask MIL to stop. Best case: you like them a lot and now you have an extra set of eyes and hands just a few doors down from the MIL you don't trust. This could turn into a big win for you.

PS 3.5 year olds don't need *that* much supervision, relative to an 8 year old. Both can play in a room unsupervised for a long stretch of time, with periodic check-ins, and the worst that's going to happen is that they make a mess with toys.