How To Make Feed Healthy Food Himself?

Hi,

i am mother of 2.5 yr old cranky boy. until now i am feeding his regular breakfast , lunch, dinner. He can feed himself if he interested. but when ever he feels hungry, he is asking for chocolates, biscuits, dry nuts & grocery eatable items which are eatable but not prepared dishes which are infront of him like dosa, puri, upma & rice. He is not at all interested to food from 6 month onwards, every time its battle to me to feed him. i offered all varieties of foods to him. he interested very few items & that too in very little quantity(max of 4 pieces) .

after 6 months, i am planing to join him in playgroup, i am worrying now how he can feed himself in that bunch of class & with in short time? How i can help him to make habituate to feed box of items himself with intrest(to avoid his morning hungry) ? even i am feeding him enough quantity food very well, he is not gaining weight much because he is not eating with intrest.