For a kid, you could just open an IRA for them as a UTMA. Although it sounds like you want to give it as taxable, so it can be spent.
Is the idea to have exactly $10k in an unknown amount of time? Or to invest the $10k to increase the size of the gift?
You could just invest the $10k however you normally would and then write a check when the time comes. 5-8 years is a pretty long time horizon. And if the market tanked, you could either supplement it or just give $5k or whatever.