I thought you could rollover a 529 plan balance up to $35k to a Roth IRA for the beneficiary. That may be easier than the lemonade stand scheme. There are some caveats like the 529 plan has to be opened for 15 years and leftover balance (including earnings) has to be in the 529 plan for at least 5 years. So it may not be useful if kid did not have a 529 plan already.
In a Roth IRA, kid can always withdraw the contributions at any point without tax or penalty.