Hi Sah,
A lot of thals I know, including myself, were fussy eaters as kids. I do not think it is the case with all thals. You would not guess by looking at me today, that I ever used to be a thin child ...
I remember, I used to love drinking fruit juices. So, try liquids like fresh fruit juices, and soups. These are easy to digest and nourishing. Try giving orange juice mostly while taking desferal, as it is high in Vitamin C which effects iron absorption. Avoid apple juice because of high iron content.
Fish is often better than prawns as it's not high in iron and is 'brain food' with good proteins. White portions of chicken is also not as high in iron. Milk/yoghurt is almost essential in order to get calcium and it has nil iron.
Some vitamins improve the appetite and aid digestion too, and it is necessary to have folic acid (w/o iron) 5 mg daily.
A very important thing I have noticed is that appetitie of thals is effected if the HB drops. If the Hb is allowed to fall below 7-8 gm, the child may feel too sickish to eat properly.
I recall a thal friend of mine, Ashish and me, when we used to take transfusions, we would get quite hungry and think of food, as the blood used to flow in ...lol...the appetite would improve with transfusions.
We would joke about it.
Anyway, take care. I hope this helps.