I have a runt (Standard not Bantam) Welsummer who I decided at the outset I would not give any extra "help" to. I decided if she could survive without any extra assistance from me, then more power to her.
The other 3 chicks I have are SO much more robust than her. She (we call her "Derf") would eat and drink but wouldn't go after the mealworms or other treats I put in there. She actually seemed to just not "get it." Within a week she finally was going after the worms, playing keep-away, the whole bit.
HOWEVER, she is still smaller than the others, probably about 2/3 of their size, feathering out just like them, she's just smaller. She seems to have these spurts of growth, so one day she looks about half their size, then the next day she's two-thirds again. Actually, like my son!
I haven't weighed them at all. It's an interesting idea.
Did you weigh them because she was so little or do you normally do that?