For very small children it probably doesn't make sense, but when they get a bit older it's not that unusual. My kids have my credit card on their phone for when they need it.
They are also joint owners of our bank accounts. We've told them if they ever get the news that we have died, they should go withdraw a bunch of money to carry them over until all the estate stuff settles.
Sharing a credit card doesn’t take an huge amount of trust. Every time a charge is made on my card, a notification flies by on my phone. If they abuse the card, I would find out right away.
They are also joint owners of our bank accounts. We've told them if they ever get the news that we have died, they should go withdraw a bunch of money to carry them over until all the estate stuff settles.