Both weight and height are within acceptable limits though slightly below average.
How is his appetite.?
Next Steps
I would just do a CBC to screen for Anemia and start iron drops if tests suggest that.
Also as Dr Sridevi suggested u can give him pediasure once per day.
He should have otherwise a well balanced diet.
No fancy supplements are needed. Deworming if not done within 6 months should be carried out.
Health Tips
iron rich food like spinach,jaggery,nuts,red meat if u are non vegetarian,peas, chickpeas,beans soyabean,lentils should be included in the diet.