Most likely it is only broken if it slipped. I think it is possible even with shavings, if the brooder is a little slick.
If that is the only symptom (leg problem) then I think a break is suspect. If there are other symptoms, I would consider what else it could be . . . .
Healing broken bones is relatively easy, if I remember correctly. But I think you have to re-align the leg PROPERLY and then bind it with something. I would google it for more information, if I were you, before doing anything. Chicken and Duck anatomy should be fairly similar. Someone here might have experience.
1. Make sure it IS broken -- look to see if the leg looks out of alignment, or see if you can feel it (probably will be difficult, but not impossible).
2. Set it properly -- that you will have to look up.
The best person I know to advise you is dlhunicorn. PM her. Hopefully she can give you answers. Otherwise search the web for everything you can find before doing anything!
I'd help, but I have to go now . . . . GOOD LUCK!
Also you might try starting a new thread that says "broken leg" if that is what you truly believe it is.