Son is Not Gaining Weight

Last weekend when I went shopping for Amish fireplace, I met a lady who was also looking at the same item. She koochi-kooed my son and he too responded laughingly. The lady how old is he and when I told her that he is 9 months, there was a look of surprise on her face. She didn’t say anything but I know that she must be thinking that my son is underweight. Which he is. He is a fussy eater. One day he likes something and next day he would vehemently turn his head from the same thing. I don’t know how he is going to gain any weight if he keeps on refusing to eat.