Kids aren't always hungry in the morning, so the best way of getting them to eat a good breakfast as to show them a good example and make it a real family moment around the table, even if this means getting up a bit earlier.
Having a good breakfast is absolutely essential for keeping their energy levels up, and according to what they eat at breakfast you can make sure they get a good balance of other nutrients at lunch and dinner.
If your child really isn't hungry at breakfast-time, start by giving him or her a glass of fruit juice to awaken the appetite. If nothing else works, toast and a carton of juice or milk on the way to school is the next best thing, but nothing can replace a proper sit-down breakfast.