this is such a hard question and it highlights a lot of the current issues with bitcoin.
Discussion
I remember reading something about a bitcoin time lock or something that did that. Can't recall exactly about it though.
My concern is the utxo size / fees
I would guess and say that in 20 years 100k sats would be so valuable that your kids would not even be concerned with fees.
Hah are fees the “new inflation”? Kidding aside it’s anyone’s guess what 20 years will look like and base chain is still probably the safest bet.