I've got a Welsh Harlequin duckling who is substantially smaller than her nine siblings -- she is growing, just waaaaayyyyy slower than everyone else. Just a word of caution, mine was in with everyone else and got stepped on several times, which seems to have caused some problems with her legs. I separated her, and she seems to be recovering, but if I had it to do over again, I would have separated her (maybe with one other duckling for company) as soon as I noticed how much smaller she was to protect her from being squished.