Try it first, if your kid can straddle the bike with the seat all the way down, I would go with the 24”. Having taught a few kids how to ride, I find the larger wheel more stable. I remember “borrowing” my neighbor’s old 26” Schwinn Cruiser when I was 7. I sat on the tank (the fake gas tank on old Schwinns which held batteries for the headlight) as I couldn’t reach the pedals from the saddle, and even sitting on the tank my feet couldn’t touch the ground. But I still had a lot of fun on that bike.