When can you put the father bunny back with the babies?

i would suggest never introducing them! if he gets near them, he will most likely kill them... sorry, that's the awful truth. i had to learn the hard way when i was a new breeder, and believe me, it's not that fun at all! don't even introduce the boys without being around. if you leave them alone, he might try to hurt them. if you do introduce the boys (not the girls because he will either try to kill them or breed with them!), do it slowly. maybe a little each day. oh, if you do do it, some time after their weaned would be the best. hope i helped.