A 529 account is a good bet if you expect your kids to go to college and want to help them with that. All earnings are tax free if the proceeds are used for college-related expenses.
Another option is an UTMA account. This is a brokerage account in your kid's name, but you make the investment and withdrawal decisions until your kids reach a certain age (often 18 or 21, but I think it varies by state). This isn't as good of a long-term tax shelter as the 529 account, but it does have some attractive properties. Each kid gets $2k of investment income taxed at normal single person rates (typically 0% for long-term gains and qualified dividends). Past that, the "kiddie tax" can kick in, whereby the kid would owe tax on the income at the same rate as if the parent had earned it instead. See
this handy page for more info. One strategy might be to transfer enough appreciated stock into the account each year that you can sell it and realize a $2k gain. By paying 0% on this gain instead of 15%, you could save $300 per year per kid on your taxes.
Do be aware that any funds you transfer to an UTMA account legally belong to the kid. Any money you (as the custodian) withdraw from the account is supposed to be used for the kid's benefit, and not on things that you (as the parent) are legally required to provide to your kid. So you can't spend the money on your mortgage or groceries or medical bills, but summer camps, music lessons, birthday presents, and other things that go above and beyond the basics would probably be okay.