M.L.
Though it is not the best idea to get them to learn that veggies are yummy, there is a great book called "Deceptively Delicious" that has recipes to get the veggies into everyday food that you eat. At least then you know they are eating the veggies, and, maybe when he is older you can show him how he had been eating it all along and he can try it in its normal form.
http://www.deceptivelydelicious.com/site/