Let me start by saying I am not a medical professional of any kind. I'm a mom with an 11-y/o daughter and a 13-y/o daughter.
My 11-y/o is built like me. She has a high metabolism, and will lead a life of eating whatever she wants. She will burn it off, stay skinny. I'm almost a decade into middle age, still skinny as heck. I hope my daughter chooses good foods, cuz it's not good for anyone to eat whatever they like, even if weight isn't gained. It is very possible to be skinny on the outside and 'fat' on the inside - clogged arteries, etc. I let her spend some days just nibbling, as long as it's reasonable stuff - nuts, fruits, whole grains. I don't always insist on "meals."
Then there's my 13-y/o, who insists she's "fat." She's almost my height (5'6"), weighs about 115 lbs., and is slightly bigger-boned than me and my younger one. The older daughter's body mass index is fine, she is simply unfit. Something of a couch potato. She tires of hearing it, but I will continue to stay in her face if I think she's not eating enough. Growing kids need good foods, at least a few times a day.
A child's pediatrician asks about habits and eating habits, and will track growth rate depending on these things, and body build. I would think a healthy 11-y/o could weigh anywhere from 60 lbs (if petit) to 120 lbs (if taller, active, bigger-boned).
About 80-100 pounds.
64 to 69 pounds
40 pounds
50
132
I42lbs
70 to 90 pounds
About 40.5 pounds to 50.5 pounds if that skinny
95kg of pounds
50pounds
109 lbs
75 lb