We've gotten a ton of use out of our membership over the last few years. It's not the biggest museum, but that makes it more manageable (and not exhausting!) with kids of any age. There's always an interesting art exhibit in the back halls and a kid-friendly traveling exhibit in the main space.
The permanent attractions, like the art studio and the giant wooden playground made it worth a visit 2-3 times a month. I recommend packing a lunch to eat outside on the picnic tables after your visit.
Overall: It's a fun, interactive, clean, family-friendly museum, probably best for babies up to middle-school age. But anyone can have fun and learn something! Oh, and their annual Night at the Brewseum (and post-event Sunday beer garden) is a great date night.