I had one of those 'skinny' bf babies.

She was 7.1 at birth, and was never over the 20th percentile on wt
charts.

At 1 year she was 18.14 lbs.

At 2 1/2 she weighed 26 lbs.

I had the opportunity to see my husband's  11 y/o sister wearing size 6x
clothes when I went school shopping with her while I was pregnant.  My
husband is Italian, and both his grandparents were very small.  His
grandmother is under 5 ft, and his grandfather was about 5'2".

So I knew the family history, and even tho she was only at 20 percentile
she stayed there, and was always healthy, etc.

She 22 now and average size, in fact has to work hard to keep her weight
under USAF weight standards.  My husband's sister is still very skinny,
wears a size 4.

I think instead of looking at what's 'average' we need to look at what is
normal for each baby/family.  My daughter's ht and head circumference
were always on target even if her weight hit a plateau.  She was a very
active baby, cruising at 5 months, walking at 8 months, etc.

Just one opinion/experience.

Kathe Catone