It's really important to make sure your child eats healthy. Introduce fruits and vegetables early on so they'll become used to the taste of things like peas and carrots and watermelon. Sometimes you have to introduce a food to your bundle of joy 14,345 times before she will eat it. But it's so worth the nagging and screaming because you know you are doing the right thing and your daughter will totally thank you for it later.
I suppose it's OK to give them a treat every now and then. But be warned: things like chocolate and sugar can alter the behavior of your offspring.
It's also important that you set a good example and eat healthy, too.