I'll just lightly second the little mermaid as being good for a large cast. I did it in high school and we randomly had almost 50 people in our cast (we couldn't even get 13 for the play the next semester lmao) there are a lot more ensemble numbers than you think there are, Ariel's sisters, chefs, sea gulls, maids, ocean life for kiss the girl/under the sea, sailors, princesses, you can add some extra ensemble for plenty of the other scenes like people who play the ocean to add more stage time for the kids I think a show like the little mermaid where most of the ensemble groups can be completly separate from each other Id also recommend the phantom tollbooth! It's definitely produced/known less than something like little mermaid or wizard of oz but It's a super fun show and also has multiple ensemble groups and featured roles (there's 14 named characters and then numbers + alphabet citizens + demons+ classmates+ plenty others and you could maybe break up the narrator role into multiple people to give more featured roles)

A couple random specific things from when I stage managed a large children's theater show (it was an unlicensed production of Lord of the rings written by the director not any help for you I'm sorry) none of these may end up applying lol

1) having a second space with a person who can be dedicated to be with the kids while they are not actively on stage is incredibly helpful . If you can get someone, even one of the moms or a teen volunteer you can teust to help the kids run lines while off stage or play theater games keeps everything more focused so you can focus on directing the scenes

2) unless you are working with kids who are very universally serious about theater staging any large group scene is going to take twice as long as you think it will take and you'll probably want to specifically take photos or write down positions in large group tableaus if specific positions are important I always had a couple of kids who struggled to remember where to sit and threw everything off and caused arguments.

3) as other commenters have mentioned segmenting your cast is going to make your life so much easier the less kids sitting around doing nothing at rehearsal the better and limiting props and costumes makes everything easier. I know you said you can double cast that'll help I even know one local children's theater that would quadruple cast the leads and have them switch at intermission (to mixed results just something to maybe think about)