For MK we always take advantage of the early entry morning. In 1 week it occurred twice for us a the end of June.
We arrive at MK around 7:45 AM - do many rides, Fastpass Splash a little after 10 am to get a return pass for 1 pm to 2 pm, then do a late breakfast/early lunch at the Plaza Restuarant or Crystal Palace, after eating and a ride do Splash and go to another Park in the afternoon.
We feel unrushed and have completed many rides on our list.
In the AM there are great rides open for kids (and adults)...
Attractions open during MORNING Extra Magic Hours for Magic Kingdom:
Buzz Lightyear's Space Ranger Spin
Cinderella's Golden Carrousel
Dumbo the Flying Elephant
"it's a small world"
The Many Adventures of Winnie the Pooh
Mickey's PhilharMagic
Peter Pan's Flight
Space Mountain
Stitch's Great Escape
Tomorrowland Indy Speedway