Hello mam - maintaing weight is matter of dynamic activities, proper low calorie without fast foods diet. In this age he need more protien, less junk. Give healthy foods always with good outdoor games..nonstress but timely working/ study all are equally well balanced need.About height you need to provide best quality protien rich products, dairy more, pulses, vegetables, greens, fruits also. You can v supplement like Protinex two times.
At 11, your son is nearing his growth spurt in which you might see his height growth. His Adult height will be mostly decided by his genes but proper nutrition and physical activity during this period helps to maximize growth. Indulge him in athletic activities which will help to keep weight in check. Limit intake of junk and easy munching foods like chips,b burgers, wafers, cheese balls etc. Include fruits, veggies, nuts, eggs, fish in the diet. Interesting recipes which attract teens like fruits chats, puddings, sprouts bhel, whole wheat pasta with veggies, fruit jellies, hummus with multigrain bread should be included so as to keep them interested in home food. Lastly, exercise, exercise n exercise ...that's the best remedy to watch his weight.