Talk to Pediatrician on Underweight Kids

Hi. My kids aged 5 and 4 are under weight; 4 and 3 kgs respectively. They don't want to eat no matter how hard I try. Hardly adhi roti khaty hain. They're super active all the time. I do incorporate cheese, oats, egg, roti, meat, milk in their daily diet in some form, chahy thora sa hi ho. I was wondering if I can give them pediasure to achieve their weight goal? May be doodh m mila k instead of water? q k doodh k elawa dena mushkil hai.