There is nothing to worry about. His weight for age is normal. It is natural in boys to gain height at this age. The weight also increases simultaneously.
Try to maintain a healthy and balance diet including all the nutrients like carbs, proteins and good fats. Make home cooked meals which includes fruits and vegetables, milk and other dairy products, eggs, whole pulses and cereals and nuts and seeds. Avoid processed foods and fried foods for better growth and development.
Next Steps
Keep a watch on weight and regular activities, if weight goes down or don’t see any improvement you should consult than else you can wait for sometime
Health Tips
It’s natural phase you can just plan balance and normal diet