Thought I’d share a good option for 24" bikes. We got one of these:
Works great and did not require an adapter for kids wider 24" tires. If using narrow tires on 24" wheels, may need the small wheel adapter. There are caps that are needed to replace the QR ones if your hub doesn’t have QR.
Found used ones on ebay, but you can get them direct from Kinetic and currently had free shipping. (Apparently I caught it on sale for 399)
Nice thing is that as kids upgrade their bikes, this can stick with them…
Figured I’d share for others that were in the same boat.