Actually, I never liked the idea of Keyfobs, especially not to kids.
They are even worse than keys since they usually also turn off the alarm at home.
And kids tend to loose things, and criminals have started going into schools to steal keys and phones, then go to the house and empty the house.
I recently got hold of a Yale Doorman door lock, it does not have a key, instead it has a tag reader and code pad, unfortunately it is not able to communicate with Zigbee or Zwave yet, but I hope it will come eventually. Currenlty I can use my cell-phone with an app to manage the lock, but I hope I can integrate it with the Home automation later.
But it has one very clever feature.
By default you can assign a 6 digit code, or tag+4 digit code.
So I give my kid a 6 digit code, no keyfob or key to lose or get stolen at school, but they can get in and out when outside playing and someone is at home.
I also have a 6 digit code myself that I can use so I don't have to pull out the tag every time I need to take out the trash.
But when the last person leaves the house, they activate the away mode by locking with the tag+4 digit code.
This not only prevents the lock from opening from the inside, but it also blocks opening with only the 6 digit code.
So even if the kid by accident tell the code to someone, they won't be able to get in as long as no one is at home as you can only unlock using tag+4 digit code.