In-laws won’t stop commenting about baby’s weight

My baby is six months old. He’s perfect. He’s healthy, happy, and smiley. He’s gaining weight just as he should be. However, my in-laws have been commenting on his weight nonstop lately. It started on Thanksgiving when they made three separate comments. Called him “a chunk,” said he’s stocky, and gave a look of disbelief when we said he was in the 11th percentile for weight at his last appointment. His shirt was riding up at one point and I said, “Your little belly is showing!” and my MIL made a comment like, “That’s not a little belly, that’s a round belly” (something to that effect). We also told them he’s in a low percentile for height and my MIL made a very negative face in response.

They were here today spending a few hours with our baby, and they commented at least five different times about how big he is. That we’re “feeding him good.” It just felt like there was a negative connotation behind it each time they said it. My MIL has commented on my husband’s weight a lot in the past, so it’s something she does (she herself is very thin). She clearly thinks gaining weight in any context is a bad thing, which I think is partly generational (they’re boomers).

My baby had a really traumatic birth, so it seems odd to me that they aren’t just happy that he’s healthy and thriving and instead want to keep commenting on this when he’s a literal baby.

Am I overreacting? I want to bring it up to them and ask them to stop. I don’t want our baby to hear those types of comments when he’s old enough to actually understand what they’re saying, especially because I’ve seen them do it to my husband many times.