If you're wanting to save for future education costs, a 529 would be the best tax advantaged option. For more general purpose investing, a UGMA account would probably be what you want. Do keep in mind that kids assume ownership of UGMAs when they turn 18 though.
As for funds, just invest in any mutual fund or ETF that tracks the S&P500 if that's what you want. VOO is a popular vanguard ETF.