Theres lots of tips on legoland on sites like rollercoaster.ie - go to the holiday forum.
I was in legoland Windsor last month and really enjoyed it. We brought Young Sully who is 3 and she had a great time. Make sure your kids are over .9 metres in height as that is the minimum height requirement for many of the rides...some need them to be taller again. Also bring a change of clothes, many are water rides and you do get wet.
It doesn't have the magic of disney but it does have the wow factor with more thrill seeker rides and so on. I really enjoyed it and only for the recession, I'd go again!