If the kids have no concept of money, then in theory the best thing to do is to either place it in their piggy bank, or to ask them what they would like. Straight buying them presents with it isn't wrong, but in theory the money itself presents them with a choice in what the gift they want should be.

If it's a few bucks it goes into their piggy banks, if it's like dozens or a hundred dollars then it goes into their bank account

personally, depending on their age and the banks rules, I would open an account and dump it all in there. I wouldn't touch it or let them get at it until 18 (or if they emancipated for some reason, obviously), at which point it all becomes theirs no questions asked.

whenever they get a job and earn their own money, that's their own seperate deal and I would encourage them to have their own separate account as well, to try their hand at earning and managing their finances. but the other account would just bank until they turn 18. I would even consider telling them you will match deposits to that long term savings account up to a percentage or total amount per year.

a shot of cash to pay security deposits or a meal plan or whatever at 18 is a really big thing and it's very instructive to see how fast it can vanish too if deciding to spend it on ephemeral things.

if you help them with those "moving out" or school/food things, then it's a down payment on an e-bike or a sweet gaming rig or a gap year trip or whatever. the idea is they have a wad of cash that becomes theirs upon legal adulthood and they can officially blow it on whatever they want. like a rite of passage.

money and money management is an under developed skill and the cost of lessons learned late can be cruel. might as well establish some concepts and familiarity when there are guardrails and the stakes are low.

Whenever it's a large enough amount of money ~$100, I usually just drop it in my bank account and put that amount plus a bit extra in an education savings account. My kid is still young enough to not really understand money.

my grandmother used to buy me premium bonds when i was little, dunno if something similar exists where you are but essentially it's like putting some money aside in a lottery fund where you might win something, but even if not, you still have the original deposit however many years later when you withdraw it

I always got to keep the money and buy candy or toys

Buy Bitcoin