My kids are 5 and 1, and the 5-year-old is 44" tall, so our situations might be a bit different. But my MK FP+ choices are:
Day 1 - Mine Train, Space Mountain, Enchanted Tales w/ Belle
Day 2 - Big Thunder Mtn Railroad, Splash Mtn, Main St Electrical Parade
MNSSHP day - Meet Tinkerbelle, Meet Ariel, Meet Anna & Elsa
(I really only wanted the A&E meet for our party day but you have to choose three FP+ so I just picked anything for the other two. I might change them if we've already done those meets on our other MK days.)
My plan is to ride the "all ages" rides - Small World, Peter Pan, Pooh, Jungle Cruise, Pirates, etc - at rope drop when lines are shorter. Then use the FP+ for the headliners.