Definitely Peter Pan! Followed by Alice in Wonderland. The other Fantasyland 'dark rides' can get backed up with 10-20 minute wait times pretty early in the day, especially if DL has early entry like on Tuesdays, Thursdays and Saturdays.
ToonTown is another popular area that I like to get done early. It has very little shade, so if the kids want to explore the homes of Donald, Goofy, Chip and Dale, Minnie and Mickey and hit the Gadget starter-coaster or Roger Rabbit, I'd recommend hitting that area before it gets sun baked and toasty!
Bugs Land in DCA has a nice little sprinkler/Splash park area mixed in with their rides, and that area is usually not too busy.
The two carousels are beautiful and usually have short lines, and the pictures are priceless, especially the King Arthur one with its castle background. Speaking of the castle, I bet the kids would love to explore it!
I love stalking the DL app, even when I'm not planning a vacation! You can get such a good feel for traffic flow, watch when FP'S run out, see what closes early for parade and fireworks prep and I love that they just added all the menus, which makes finding food nearby easy without visiting each restaurant to read the menu.
Have fun planning!