The doe is likey already pregnant again. Bucks find does give birth attractive for some reason, and does can get pregnant right after birth.
Sex them and immediately separate them
https://www.raising-rabbits.com/sexing-rabbits.html
I'm sure it's quite cold where you are, so I would bring the mom and babies indoors. She'll only feed them twice a day (once in the morning and once in the evening). Which means you can separate them now, even before sexing.
Leave the mom and babies alone after sexing the parents and checking checking be sure the babies are healthy. They should have full and plump bellies.
You can feed unlimited Alfalfa hay and pellets for the mom, and the babies will start to eat it when they're older.
I would go ahead and schedule an appointment to get the male neutered.
What type of enclosure are they in?