Y.W.
Islands of Adventure has a lot more of the thrill, high speed rides and of course the Harry Potter ride. So if your kids are into that then I would definitely go to Islands, they probably will not be able to ride the coasters (3) but should be able to do the rest. Universal has all the movie rides except for the two coasters, plus they have shows. Also, I think that right now they are doing the holiday parade at Universal so your family might enjoy that too. Honestly you will be on vacation and any park you decide to go there will be enough for the whole family to do. Enjoy your time in Florida!