I brought my 4 year old and 2 year old there. They...

I brought my 4 year old and 2 year old there. They loved it, due to time constraints, were only spent two hours there, and we didn't quite see or play with everything we wanted to. I think three hours would be a reasonable amount of time to explore (assuming your kids are about as young and curious as mine). Most everything is 'hands-on', and I myself enjoyed the experience.