[Powlay]

I think the one person who may get bored with 21 days in disney is the 16 year old. There are really only a couple of rides in every park that will suit a child of that age.

MK - Space mountain, thunder mountain, 7DMT, splash mountain
AK - Avatar, rapids, everest
HS - Rockin rollercoaster, tower of terror
Epcot - Test track, soarin

There will be more than enough to keep a 4 year old and 17 month baby entertained.

Would there be enough at Universal to entertain the littler kids whilst the 16 year old rides the bigger rides? Id say yes and no. We've just returned and did disney and universal and had a 21 month old baby and at universal there wasnt much at all. Red fish, blue fish and caraseussell were ok, other stuff were all 92cm. Shreck we did also and then it was basically lots of looking about and self entertaining with characters and play areas.

But the 17 month child will sleep at times when you can go on rides with them so...