we took rich 5yrs ago so thats when he was 5/6 and he enjoyed it, i took him about a year before and apart from running off, first and only time he has done that, he really enjoyed it then.
it depends on your son hun, theres lots of rides, but if you going in school holidays theres lots of queues which isnt the greatest for little ones to wait, theres places to play with lego etc and some things to walk around made of lego.
i'd have said he would enjoy it, but he would enjoy it and get more out of it in a couple of years