I would make them their own pen if you plan on breeding. A lot can go wrong that's just not worth risking imo. It's one thing to have a buck in there, he'll hump chickens and maybe play chase if ornery. A doe will become defensive as she matures and breeds. She could harm a curious chicken. The buck could harass her stressing her while she's nursing, impregnating her after kindling making it so her 2nd litter is born before she's weaned the 1st one. The feed can be an issue long term too.
My chickens eat mice if they catch one, baby bunnies are meat snacks if small nuff to a chicken. A friend of mine had young chickens in her rabbit pens and baby rabbits ended up missing toes from chickens who saw just a lil wiggle and bit.![]()
In with chickens is not the safest place for baby buns.
x2 Some bucks won't even wait until the doe is finished kindling to try and breed her...