Don't expect a lot of availability for the big rides later in the day, especially at the non-MK parks (and at MK, Seven Dwarves Mine Train). If you schedule your FPs for around mid-day you might be able to snag a thrill-ride for later. Try to hit them all at rope-drop and earlier in the day. With hoppers, I'd still schedule for the second park though.
If your kids are old enough, there is always the single rider option for certain rides (Test Track, Expedition Everest, Rock'n Rollercoaster) if you are comfortable with that (it works very well for TT).
When are you going? Lighter crowds will give you quite a bit more flexibility, but heavy crowds mean those FPs are going to get taken up rather quickly.