First quick answer: don't pay for your kids' education. And make that point clear to your kids. My parents didn't pay for mine, and as a result, I was well-motivated to work hard in High School so that I could get scholarships. The same will be true for my children. There are tons of grans, scholarships, and low-interest student loans available. It also reduces the risk that your kids will waste that money (sad, but often happens).
Basically, if you're saving that money, it will go to one of three places: A) your kids' college expenses, B) your retirement (keep in mind the possibility of nursing home expenses and the like!), or C) your kids' inheritance. If you opt for A, then you lose your control of that money as soon as your kids use it for college. If you save it for B/C, your kids may still get the money, but you'll be making sure that your own needs will be taken care of first. I don't know about you, but as much as I love my kids, I don't want to be a financial burden on them when I'm older, nor do I want to take the risk of making myself dependent on them.