It really depends on the broody. Some will not, but some will. I have a broody right now raising two chicks who are almost two week apart in age. One is now 6 weeks and one is 4 weeks. I had incubator problems and a dissapointing one chick hatch and did not want to leave him by himself so I gave it a try. Momma Silkie was originally sitting on 3 eggs and only one hatched. She's a great momma and I have had zero problems with the age difference in the chicks.The big one doesn't pick on the little one and momma keeps them both in line. BUT some broodies aren't even good with their own chicks let alone new ones, so if you decide to try it, keep a close eye on them at first and have a backup plan for raising the chicks if she won't take them. . .