Why is it people judge a mother based on the size of her baby?

I have seen this too, in several different ways, with my own babies. My oldest (a girl) was born when I was very young. People tend to think young mothers don't take good care of themselves. I gained the 30 pounds and ate really healthy but she was still only 6lbs 6oz, three days late. Naturally people assumed it was my fault. Four and a half years later though, I proved everyone wrong in a way when my 2nd daughter was born. Again, I ate healthy, gained 42lbs which is a lot for my normal size but she was still only 6lbs 8oz (6 days early). My girls were just meant to be small babies. (another common assumption is that young moms have premature babies, obviously that wasn't the case with me either). My weight gain has never had anything to do with the size of my babies. In fact I struggled to gain the 30lbs with both my 1st and 4th, one was 6lbs 6oz the other was 8lbs 4oz (boy). Since with #4 and #5, I gained 30 and 33lbs respectively, it was assumed they would be small, wrong again, they were 8-4 and 8-8. Another good example is with #2 and #6, both boys, both 7lbs 5oz. I gained 38lbs with #2 and over 45lbs with #6. (another thing about the girls though, I said "my girls" were meant to be small but their father has since had another daughter who was a week late and only 5lbs 15oz, so it may have been his genes not mine after all) Right now a common misconception we're dealing with involves the paternity of #4 and #5. They really do have the same father, no doubt, no other possibility. But people assume that they must have different fathers because #4 is small and thin and #5 is tall and pudgy. (they are 4 and 2 but both are the size of an average 3 year old) Their father, although average (and slightly "chunky" now) size as an adult was a very small child. I was a very large baby/child until school age and am now quite petite (5'3" and normally 105lbs). I guess some people can't believe that a son could take after his mother. I think people assume these things because of a lot of reasons. Some are common misconceptions like small babies come from mothers who don't eat enough and large babies' mothers over ate, completely forgetting about genetic factors that determine a baby's size. Also some people just like to judge others. They tend to be the ones that insist their way was right. If your baby was bigger than theirs, you must have eaten too much or fed the baby too much. If your baby is smaller than theirs you didn't take care of yourself or the baby properly. It's a sad part of human nature that feels compelled to make arbitrary comparisons based on only partial facts. If they aren't comparing size, their looking at development. It's no wonder parents get so stressed out over their children.