My 23 mo old is 17 lb. She’s just little and has always been off the growth chart, but perfectly proportioned. If she looks sickly I’d worry, if she doesn’t I’d chalk it up to genetics.
My first was always off the growth chart and I took him to specialist after specialist (because his ped told me too), including cardiologists, and they told me kids are allowed to be small. So after my girl took after him I just went with the flow. Also, now my son is a brick s*** house. He’s a solid boy, but it wasn’t until about 2 1/2.
He was 27lbs!