bitcoin for children

hey everyone, i need some experienced opinions on how to do this best:

i am investing in bitcoin myself and for each of our children. at the moment i have all bitcoin combined on my trezor safe 3. i am planning to give every child it's own bitcoin when they turn 25 (so we are talking about a span between 12 and 25 years here). to not get confused over time and to be able to give every child their own keys when it's time i need to seperate the amounts now. what is the best way to do this? do i just create a hidden wallet with a passphrase under my seedwords for each child? or would you recommend something else? and correct me if i am wrong but in my understanding as soon as a child turns 25 i give them the seedwords + their passphrase, they can then recover their wallet and only have access to their individual funds? thanks in advance