What an interesting thread! Excited to see what happens next. It's so great for your kids to be exposed to/learning all this.
I have a slightly similar situation going on at my place, but with two silkies. Earlier this year, one of my hens went broody. She is very bonded to one of my roosters, who was getting in lots of fights with my other roo, so I separated them in the broody pen together, intending to move him somewhere else before the chicks hatched. I lost track of time with the brood and they hatched earlier than I was expecting. My rooster seemed to be okay with the chicks, so I decided to leave him, but keep a close eye on them. This hen is also a very fierce broody, so I figured the chicks would be okay.
The rooster has been a wonderful co-parent to the chicks, calling them over to eat and letting them snuggle in his feathers. They are almost three months old now, so it's just about time for the parents to be integrated back into the flock (chicks will stay in the broody/grow out pen until they are old enough to join the flock). This morning, I let everyone out to free-range and noticed that only the rooster was with the chicks, acting even more parental than usual (sticking very close, escorting them around the yard, still calling them to food). I looked in the nest to see that my hen had gone broody again.
Before now, I'd never heard of roosters taking on older clutches so that the hen can start a new brood, but I think that might be what's happening with them.