I will throw another idea in
With 2 young kids why don't you stay in the Royal Pacific in a family room for 1 night the day before you go in the parks
Get an extra magic hour and walk straight in olivanders. We did that last week and were the only family in there at 8am. Both our kids were like VIPS doing the experience together.
You can do that not worrying about queues growing anywhere else because your room key is your fastpass for all the rest of the rides
With Harry Potter fastpass you still walk through vast majority of the theming. You just don't have queues whilst you do it.
Then get the train to the other land and again visit everything with no need to hurry. Then back again and do the HP rides again with the express pass. The train ride is a different experience both ways so you need to do both ways
The jimmy fallon ride ride fun
Spiderman is great
Mummy not as good as I remember from before
Men in black is good
Jurassi park ride is great
Kong is amazing but maybe too scary
Hulk and ripride rocket great but way too big for your kids I'm sure
Simpsons is great and then all the suess rides for young kids
When you cost up a night in the royal pacific agaisnt the cost of fatspasses how does it work out
But that extra hour in the park at the start is fabulous - especially if you take them to olivanders first whilst the rest are on the rides. That's special.
You would have a magical unhurried day you will remember forever rather than having an eye on where you need to be next and how quick you need to be there