re: What would you do with your kid’s savings account?

They need earned income to contribute to a Roth IRA. Your income isnt a factor.
If you are suggesting opening in Roth in your name instead, you could backdoor Roth (unless you have traditional IRA in which case pro rata rule and taxes would apply.) You should do this for yourself not as their Roth though.

I'd still consider 529. It can be used for college or trade school and other education expenses and worst case change beneficiaries, rollover to Roth IRA in 15 yrs (whole point is long term growth anyway so why does it matter when?), or take the penalty.

Otherwise, just use a UGMA or UTMA Fidelity Learning Center UTMA UGMA
First $1250 earnings are federal tax free and next $1250 is taxed at child's rate. It would be least restrictive to spend as needed and they could even use to fund their Roth IRAs later while in low tax bracket (perhaps even paying zero LTCG). You could even seed the account with appreciated shares from your own taxable accounts assuming if they sell as young adults they will be in lower tax bracket than you are now.