Ditto on what Damo said.
If it's The Wizarding World of Harry Potter ithat is your focus then I would be at either at Universal or Islands of Adventure at rope drop.
If you head to Hogsmeade in IOA then head first of Forbidden Journey then Flight of Hippogriff then Dueling dragons.
What a lot of people don't know is that if you don't want to ride FJ can still do the walk through. Get a butter beer
Walk around the shops. Then catch the Hogwarts Express to Diagon Alley and head straight to Escape from Gringotts. If it is really busy then come back later in the evening sometimes it eases up a little in the evening. The experience at Diagon Alley is really awesome later as it starts to get dark. You can use single rider line if needed to get through Gringotts if it's really busy.
You need a park to park ticket to ride the Hogwarts Express. Ride it in both directions as the experience is different in each direction.
Make sure to see the wand show at Ollivanders. They pick a child out of the audience for the wand show. Maybe buy a interactive wand for the little ones to do magic at both the Potter parks. There is a map in the wand box for all the sites they are able to do magic at as well as a metal medallion marking the magic spots in both Potter parks.
Have lunch or dinner at the Leaky Cauldron in Diagon Alley or Three Broomsticks in Hogsmeade. Have a great time.