8 year old son is under weight what should I do to increase weight he is a fuzzy eater

A. Okay so first you need to figure out what your child likes to eat overall as on that basis you can formulate food diet for your child and can prepare different varieties plus it’s very important that you give really good amount of protein and put your child into physical activity which would require a lot of strength energy and stamina with which the child would get hungry and will eat better