my baby boy is 9 months old and weighs 6kg,height 61cms,head circumference 41cm,he doesn't crawl and sit on its own from lying position...he can sit for few minutes without support when made to sit...what should I do?

A. The weight of the child is little less try to include more of proteins along with all the family foods in the diet of your child and slowly the weight will increase and when you talk about it one more month and if you do not able to do it on its own then you can check with the doctor and about crawl you can wait till the age of 11 months