Kids: About to be 4 & 7 years old.
Currently, kids each have a piggy bank they got while they were still drooling and could hardly lift up their own heads.. Those suckers are heavy, the thought of raiding them for grocery money should everything go hell, in the depths of March 2020 gloom, did cross my mind

My oldest seems willing to blow his little fortune on whatever the latest toy is that catches his eye, which I've been able to talk him down from a few times, but it's caused me to actually consider finally bothering with the idea of setting up the old bank account game (whether I'm the bank or we really get him an account in his name, I don't know).
My thoughts on this are 1) I have ZERO interest in going the route of UTMA account for investments after the process I went through to deal with such things from my own childhood (I'm 39 and I literally just unwound some token stock that my parents bought for me when I was like 10). 2) While I would love to be able to shove money in a Roth IRA in their names right now, I really don't want to bother with some dog & pony show way to generate earned income for them, their too young, and frankly I can't think of anything that I don't know deep down would be anything other than thinly veiled fraud at their ages.
The only obvious remaining contenders in my mind are:
1) A savings account in their names at preferably a B&M bank/CU.
Pros: Easy, no fees, has an "official" feel to it (eg. statements with their names on them that we can look at, a bank branch we can walk into to deposit/withdraw, maybe even a ledger to balance later on, etc...)
Cons: Yet another account, anemic interest (won't be any impressive compounding magic for them to watch).
2) A savings account Momma & Daddy National Trust Bank.
Pros: I set the interest rates (could make things interesting), no extra "real" accounts to manage or login to.
Cons: Will certainly lose it's luster as they get older and see through my game, lacks that "official" touch & feel of a real account at an institution.
3) A 529 account (don't have currently)
Pros: tax advantages, investment options that really can grow and impress with compounding.
Cons: Limited in scope (this is their money, I don't feel right forcing them to lock it ALL up for education, there needs to be some reward along the way afterall), paying for their education is really my responsibility anyway, another account to manage.
4) Taxable brokerage (separate account but in my name, unlike UTMA)
Pros: Very flexible, compounding magic potential, potential for portfolio/fund manager competition game later on.
Cons: Another account, small sums of money might be quite limited without MF's or fractional shares.
5) Virtual taxable brokerage (no separate account, we just virtually "tag" funds with each kids' names but they go into our brokerage account)
Pros: No extra account, no UTMA hassle, compounding magic... The way I envision easily being able to keep their funds separate is simply to invest them in different tickers tracking the same underlying (eg. IVV & VOO).
Cons: Might be a hassle to track but I'm optimistic about it.
So, are there any terrific ideas I'm not thinking of? What's worked for you and your kids? Was growth/compounding important for you/them in deciding the direction you went in? What about the hassle of managing/transacting and then finally taking off the guard rails (actually giving them unfettered control at >18 years old) for what you did with the kids?