We decided to get a family membership and I do not regret it! Our daughter is still pretty young (16 months) and there's plenty to keep her entertained for hours....the membership has been worth it because we are downtown a bit and can just pop in for any length of time. Right now our favorite room is the water room followed by the gardens - I cannot wait to see how our child's interest change with age and I know there's plenty to keep us coming back!
PS - before the kid, we LOVED the adult swim nights. Highly recommend!