This lock has a keypad, so the kid just needs to remember that. It has a key also, but if the kid never has the key, they can never lose it.

Maybe you can go a bit lower tech. There are “smart” door locks with a keypad that have Bluetooth, but are not otherwise cloud enabled. Then find a small device you can use as a Bluetooth proxy and position it near the front door, to keep tabs on it. Our lock is from Kwikset, and while there is an app to program it, once it is programmed it is pretty much stand-alone and won’t need the app anymore.

The lock does have Home Assistant integration but I haven’t tried it yet because I haven’t done the Bluetooth Proxy yet.