Do you think this is a good idea or you would still go multisig

[Thawson]

Multisig is still the safest bet here, directly splitting the seed phrases offers simplicity but very risky, the problem is the halves are not independent and losing one jeopardizes the wallet besides a seed phrase was never designed to be split in half
A 2 of 3 multisig was designed for this type of situations. You have 3 independent keys where 2 can work in hand to access the wallet. You can store the third sepetely, in a situation where either the dad or son lose their key, there is still a third key as safeguard.

The reason people use 2-of-3 instead of simply 2-of-2 is because it provides redundancy.

With 2-of-2:

Lose one key = funds are gone.

With 2-of-3:

 Lose one key = you still have two remaining paths.

[ColdLava40]

What do you think? Someone asked this of me yesterday.
I think it's more simpler than the inheritance idea of multisig 2-3

I was just thinking of a case where the other part of the splitted seed is lost by one party, either the father of the son. How then would they recover it? Don't you think this creates a single point of failure?

It's sounds like an idea but not a good one. Multi signature wallet still remains the most preferable in this case. Although with your idea, it would be impossible for any party to spend the coins without coming in contact with the bother party. But a lot could go wrong.