first check out few things like: intestinal worms(very common and very bad for health), water intake(at least 1litre fluid daily), calcium intake(u can give chewable tablets-for kids, like sandoz), motions(constipation/ loose motions, both affect appetite)
some ideas for meals:
-whole wheat bread instead of maida bread (the ingredients on the packet should say 'whole' wheat, not just wheat)
- whole wheat pasta and veggies in white sause (coarsely mashed)
-maggie with lots of finely chopped veggies
- paav bhaaji- with less spices of course (it is an excellent source of all veggies)
- make a powder mixture of almonds, cashewnuts, pista and walnuts. add it to milk while boiling. strain it before u give the milk.
- same mixture in all kinds of porridge u make for him(sooji, saabudana, ragi, oatmeal porridge)
- honey, instead of sugar, in milk
- mix boiled potatoes/ carrots/ peas in dough for his chapati
- aatta chila, besan chila, soyabean chila with tomato-ketchup faces on them
he may not be liking the taste of the food u serve(hard to believe!). some children are more fond of sweet dishes, while some like spicy. find out what yr son likes more..(chocolates or spicy pickles!!) that will guide u how to serve tasty items with hidden nutrition
invite his friends over for snacks/lunch..kids tend to eat better when they see other children eating
do not serve big portions. kids get turned off by seeing huge servings in their plates. instead serve little at a time. do not insist or cajole him into 'finishing' the meal. kids do not like the pressure to finish. in any case, do not make him feel guilty for not finishing. he will eventually pick up from here.
check out recipe books for kids by tarla dalal, juhi agrawal.
(pssst...your son may have a natural disposition towards thin body-structure, in which case, he is less likely to gain much weight...also, check out with the doc if he is really underweight..we moms tend to perceive our babies as underweight, if they are not too fat!!)