8 year old granddaughter- Universal???

[SwanVT2]

I completely agree with everyone who says do Disney first. Let her have that first immersive experience. There is plenty of time for Universal.

 

[Pooh's World]

I would say do both. You are there for 7 days not 3 days, so that's plenty of time to do both. You only need 2 days at Universal tops. Probably can do all the Harry Potter in one day with a park to park if you go at rope drop and then stay till night.