I was there last Memorial Day (and will be again this year). I really didn't find it to be as crowded as others are saying. Walking through the parks seemed crowded, but I don't remember any huge lines or anything. It couldn't have been that bad or else I wouldn't be going back at that time again.
It was warm, but it rained almost everyday which really helped with the temps. As someone else said, go for it, much easier to get around with just the girls!