We had to leave home at 5 a.m. for a 9:40 flight. The airport is about 90 minutes from where I live, and then there's security time, etc. My boys got up and got dressed, and while I was driving they had bottles of milk (that could be tossed after parking) and packages of donuts to munch on. When we got to the airport we got breakfast at McDonalds. We had time to eat while waiting for our flight.
However, at 3, even donuts and milk wouldn't interest my kids. I think I'd take along disposable cups with Carnation Instant Breakfast. If the kids were awake for the drive, they could sip on it. Security is so finicky that they won't let applesauce, yogurt, etc. through. I couldn't think of anything dry that could travel for nearly 2 hours and still be edible. There was even some fruit in the "confiscated items" tubs. If you don't mind junk food for breakfast, grab something fast at the airport. If you do, take along those individually sealed bowls of cereal and purchase milk at the airport. I wouldn't risk traveling with dairy or meat.