Take the time out to see a financial planner. It will save you alot of time performing your own research and they are really in tune with how the markets are behaving relative to investments now. They can sit down with you and do a 20-year projection on what college for your two children will cost, factor in your salary (and proposed increases) over those years, and then discuss with you what you have to put away each year to make your goal of sending them both to school.
Once you have the dollar figure, they will perform a calculation on how many of today's dollars you need to give you the inflated future dollar figure you desire. All in all, it's a great exercise for you and your wife to go through. Even if you weren't saving for college, perhaps it's retirement, this is a great way to get a handle on what you need to do the next 20 years to be comfortable and retire happy.
"He who fails to plan, plans to fail". -- Old Proverb
Good luck to you!