I've only heard about it in relation to head injuries and then it's sudden onset. I didn't know it was common to have otherwise! Do you know if they always have it or if they grow out of it?
My good friends second baby had this. I won't lie that the pedi was concerned because there are a few bad things it could be. She had to take him to a specialist and he turned out to be 100% fine and is now a crazy kindergartner . But it was stressful for them for a bit.
It was 5 years ago so I don't recall the details but am happy to ask her if you have questions . Definitely have her get it checked out. It's likely fine, but always good to be safe .
Yeah, I remember the size differentiation/millimeters matters. Hopefully it's nothing, but I'm sorry it's a worry! Babies are damn stressful enough without these things.