We have both in our house (DD is almost 5, DS1 is 3.5 and DS2 is 1) and the duplo is wonderful for my DSs to play with together. DS2 loves the noise it makes and is constantly tipping it all out and then DS1 will build something with it all. DS1 isn't quite up to Lego yet. He will sit with Daddy or me and help us with his Lego but he's not quite there.the duplo is different. I'm really glad we've got it. Even DD comes over and builds things with them when the boys start playing with it.