really small chick not growing

[chickencity]

i got all my chicks at the same time form the same place. they all looked they same and were the same size but i have noticed that one of my sexlinx is not growning. all my chicks have the wing feathers and tail feather but this one still looks like yellow baby chick and is mucj smaller. could a banty have gotten mixed in or is it something easle? ill got get a pic and post it

 

[Katy]

Every once in a while I'll have a chick that just does not grow. The last one peeped ALL the time not matter what. I think they're just "failure to thrive" chicks and something is wrong internally that we can't see.