In my case I just want my kids to be able to see that chicks come from mommy's, not incubators! I want them to see a little head poke out from under a hen at least once.
So if they go broody towards the Fall, and the rooster is fertile and doing his job correctly, does that mean that even at less than a year old they can have chicks? For instance, your 5 month old that is trying to sit on that 1 egg, do you think it would hatch if you let her? Sorry - newbie questions, I know. I always assumed that spring was the only time successful broody hatches happened, I don't know why.
I had a broody successfully raise chicks (and a duckling) in the dead of winter. Spring isn't the only time they can do it, just one of the best. They can brood and rear any time of the year. The winter chicks would run about for a minute or two, then duck under their Mom to warm up, then do the same. Hens make good heaters for their chicks, heh. All mine are less than a year old right now.
Provided the egg is fertile, it would hatch under a 5 month old no problem.