Yes, it is certainly a gamble. Might pay off, might not.
Why gamble with your daughter's college but not your son's?
With something "term-certain" like college where you know you want $X at year Y, I would recommend either saving more, or telling your kids that they'll get less, or some other plan rather than increasing the risk level on the investments, especially if that risk level made either me or my kids' mom uncomfortable or exposed me to significant downside risk that I wasn't willing to cover some other way.
If you're both on board and you're absolutely willing to take out a HELOC or withdraw from retirement or get a second job delivering pizzas to fund your kids' college if for some reason their account drops 30% or 50% when they are a high school senior, then maybe.