Get a master seed using the favourite hardware wallet of your choice and then derive sub account seed (BIP85) for each of them based on their dob or something. You can then hand them over the seeds someday but if they lose them you can get them back for them.
Discussion
This is a decent idea. You will want to plug the seed into a hardware wallet to export the XPUB to a software wallet like Sparrow or Nunchuk so you can generate receive addresses to send them corn, though.