key is to find the kids with the parents that are fun to be around, and essentially make your kids be friends with their kids. basically instead of a kid play date (hated typing that) you organize an adult hang out, and the kids naturally get to play with each other.
^bingo. trouble is all my friends that meet that criteria either don't have kids, or their kids are nowhere close to mine's age, or they live like a thousand miles away. sure i (a middle aged man) could go actively seeking out new friends but what am i some kind of psychopath?
key for myself is youth sports. instantly have a bunch of kids that are your kids exact same age! pick out the parents that seem cool, talk with them during a practice or game. they seem cool, YOU ARE IN!