How would you set up a trustless process to buy a small amount of bitcoin ($10-$20) monthly to hand to someone in 16 years? 

Challenges:
Avoiding hardware signing devices
Avoiding/limiting manual processes monthly
Avoiding co-mingling of personal sats and gifted sats
Avoiding the password/keys being in the custody of the parental guardian of the receiver (a toddler)
Avoiding economically unspendable UTXOs and UTXO management frequently
Would like for this to be automated.

This would be for a God-parent to gift to God-children when they come of age. 

Could you use lightning via Strike and zaps with a Nostr private and public key pair? How would you do this?