If you are not a numbers person, you need to be talking with someone who is a certified financial planner who can guide you in the right direction.
My hubby is a numbers man and our daughter is 15 and fully funded, however, we still talk to our financial guy for the "reality check" to make sure our plan is going to be effective.
Also, there was a plan years ago in TX, and probably still is called TX Tomorrow fund and people were throwing money into it for prepaid tuition. Be CAREFUL......I've heard that plan is bankrupt right now and some people flat out lost everything they invested.
Be very careful, get yourself educated on the plans and have a professional help you.
Good luck...you are doing the right thing for your children.