If you allow him to eat chips, junk foods, cold drinks, tea, bread. You cannot expect him to be interested in a home made nutritional food. You will have to teach him to eat fruits and vegetables. Make rotis or paranthe with atta plus other flours like soya, chana, ragi etc. Add vegetables in the dough. Make mix vegetables cutlets, idli, dalia etc. Include ghee, nuts, soya, dals, paneer, egg in his diet
. Unless he learns to eat a nutritious diet, he cannot gain weight and a malnourished child will continue to fall sick often as his immunity is low.