Basic Advice for Parents of Toddlers:
You are responsible for when, where, and what to serve your child. In other words, if you don't want your child to get used to eating junk food, don't make it one of the options.
Also, if you want your child to eat at the table, make that the place where food is served.
Even if your child refused to eat broccoli yesterday, you can still choose to offer it again today. It has been said that you may have to offer something 17 times before a child will try it. Just offer it, but don't force the issue. When a child has seen it and smelled it and gotten used to the idea of it (as long as they don't feel forced), they just may decide to try it and find out they really do like it after all. (Think of the book Green Eggs and Ham, by Dr. Seuss.)
The child, on the other hand, decides if and how much to eat.
Strange as it may seem, young children know when they're hungry and when they've had enough and are full. For the child's future health, you don't want to interrupt the natural hunger cues that your child has built into his system and that he can learn to recognize. Yes, you want to be sure you feed your child healthy and nutritious food, but it's not a good idea to overfeed, either. Insisting a child continues eating after he's no longer hungry can lead to obesity later on. So can linking eating to emotions.
Other things that can affect a child's eating habits are the child's temperament and the child's metabolism. Very active children whose bodies burn a lot of calories may just need to eat more than a child whose metabolism is slower.
Children also use food to assert their independence. If you let them sometimes choose between two things -- for instance, two kinds of cereal or two kinds of sandwiches -- they can learn that they have some say in what they eat and so may not need to assert their autonomy through food.