No place doing a kiddie happy hour anymore?

Wonderland Ballroom used to; as did the Reef (RIP, now Roofers Union). Johnny Pistolas upstairs. Grand Central, briefly (and, uh, they may not care to do this anymore).

Call a restaurant that you like that has a private room and ask if they would take a booking.

You can do bowling, but the kids are probably too small for that.