Yeah I hear you my daughters came into this world underweight and were that way early on in life,
One of my grandchildren didn’t seem to be gaining weight at all. The child just stayed small and just ate enough to keep going. We were all trying to get the child to eat more, but nothing seemed to work. Parents were worried and doing the best they could but also worried that if they kept going to the doctor, they would be blamed for the low weight.
I finally put some Keifer in a sippy cup (about an inch or so) and the next morning that child started eating and over the next month was growing like crazy. I’d put a little Keifer in a cup about once or twice a weekend when they were visiting and kept that up for a month or so. After that, no more problems. I think some of the weight gain problems with little ones is that the gut bacteria has not yet developed so their milk doesn’t process properly.
I was a whole 4lb. 4oz. when I was born, almost two months early. Sometimes kids are just small, or have a hard time putting on weight for other reasons. My brother was seriously picky, and he was always underweight, all the way through middle school.