Not a financial adviser but here are a couple options you could consider:
Savings accounts: Stupid simple, but stupid low rates.
UTMA: basically invest money for them over the years (index funds, mutual funds, etf, etc.) and this account transfers to their ownership at adulthood
529: good for school, possible tax benefits as you put money in, if they don't go to school, you can transfer the 529 to another family member in need of school money help.
Ultimately it's up to you. At the end of the day, just be a good example for them in real life so they can see what success looks like outside of their upbringing.