If your oldest weren't already through college, I would have recommended that you set an amount for your kids and give that amount to each of them. I set aside $75 per month for each of ours from the day they are born. It is unlikely that it will cover all the costs of college but I am OK with that. They are bound to learn a valuable financial lesson. It they want to spend 100K for college or go to college for 6 years to get a 4 year degree, then they will find themselves in debt. On the flip side, if they are frugal, apply for scholarships, go to community college for a couple of years, work part time, etc. they could come out without any debt. Either way, they will have skin in the game and will be accountable for their decisions.
In your situation, when your 10 year old gets a little older, I would sit down with her and explain that you are contributing 20K (or whatever you decide) to her education. She is responsible for the rest. You can help her with her first car or pass one down to her. Sounds fair while still holding her accountable for her decisions.