It is normal for you three year old to only eat a few bites of a meal. You are not starving him, three year old children do that. Try some fun things with food that you think that you child will really enjoy. But do not worry yourself you are not starving your child.
Have him help you make it. Smoothies are great. You can throw a lot of nutrients in them and they feel like a special treat. Jessica Seinfeld wrote a great cookbook on how to sneak in vegis into kid friendly food.
I have read that there are some days when kids eat very little and some where they just seem like a never-ending hole. I wouldn't worry too much unless it has been going on for a while. Then check with your pediatrician.
make sure you take your child to their pediatrician, or a clinic to make sure they are alright, then if all is well I'd follow the advice thats been contibuted before my response. All seems like good ideas....
You can also try pediasure in between meals to make sure that he gets some vitamins in. They come in a lot of flavors so I'm sure he'll love it, my son does, but as long as you checked with your pediatrician. Everything should be fine some kids start out as picky eaters that's all.
Kids go through spurts, won't be long before he's out of this phase and you'll be worried he's going to eat himself to death! Pediasure is a good idea while he's in this phase, but definitley doctor time if he looses a lot of weight or starts to act and/or look really sick.
I went through the same thing when my daughter was about 3. My pediatrician told me not to worry, that a three-year-old is incapable of starving themselves & will eat what they need. -Just put healthy choices in front of her/him. She quickly grew out of that stage. Good luck! :)