Talk to Pediatrician on Chewing Problem With My Daughter

My daughter has been under weight and height since birth. she started taking solids at the age of 3 years. still she is having chewing problem. she keeps in her mouth cannot chew properly, eats one meal in two hours or so. now she is 8 years old. please guide if she has some issue with muscles weakness or what, she is growing skinny day by day beacuse of under nutrition problem of not able to chew and eat solid food like roti properly. help me with and recommend some specialist in this regard. PS: my daughter is otherwise fine, very Intelligent, but she gets some gas problems often and if drinks milk she sometimes throws up too. Thanks