Mama cat attacking her mate

Question
I have a female and male pair of cats.  She had a litter that is his.  The other night my boyfriend caught one of the kitten's paws in the door and it screamed. Our female freaked out, attacked him, then attacked our male. I understand that she was scared, but now she won't leave our male alone. He's never been mean to her, he's mellow and just likes to play. How do I keep her from trying to kill him every chance she gets other than to keep her locked up. Also, the kittens are now just over a month old and they want out to play.  Please help.

Answer
Hi Kara,
Sounds as if  you are right and she is protecting her babies.
I am not sure how large your home is but you can keep the cats separate and when the kittens are weaned do a proper slow "re-introduction" with the male and female.
Make sure for now, they all have adequate exercise with the mom being able to get away from her kittens if she needs to and then return. But, do keep the male and female separate until the kittens are weaned.
The "re-introduction" technique is about building up positive experiences between the cats so they always associate each other with something positive.
Don't start this until after the kittens are fully weaned.  Her protective hormones will have calmed down by then. I like kittens to stay with their moms and littermate for at least 11 weeks even though they my be no longer nursing much earlier. Don't keep her cooped up especially when the kittens are learning to enjoy the world, she has things to show them and she needs comfortable and adequate space to teach them and get away if she wishes.
When you "re-introduce," first you start with placing food on opposite sides of the door when you are feeding them so the male and female always associate the other one's scent with something good like food.
You can play under the door with both of them with separate toys. Always make the environment relaxed and positive.
And the idea is to always have something good happening for her when his smell or presence is around so her brain is being trained to associate him with positive things.

Next step, you can switch their beds around so they sniff each other's scent.
If one is uncomfortable, or gets crabby go back a step-don't push her to go beyond where she is ready.

Then eventually you have them trade rooms. She gets his area for the day, then back at night or however you would like to set it up.
When they are ready and their reaction to each other is smooth-
Next step open the door a crack so they can smell each other, close the door if she gets upset.
If no response but sniffing then leave the door open, a bit longer, do this in intervals of a few seconds, building on the time if she acts positively.

Remember you are training her to have positive associations every time she sees him. So treats and pets under the chin, and soft, sweet admirable words to her are important, as well. Do this for both of them.
Then eventually, one kitty goes into a cat carrier (protected) in the middle of a living room during tv time or calm family time for short intervals. We build up the time with 5 minute increments if it is positive, if negative we take a step back.
Make sure the kitty is cozy in carrier and happy. If there are positive responses we go with it, if not, we redirect the attention with a toy.
One is in the carrier, the other is free in the room to explore and sniff around the carrier. Start this at five mnutes the first time, if positive, the next day time ten minutes..., then fifteen, etc...Then when they are all happy in each other's presence-you can let them free with each other under supervision...
Each cat is different, with some it can be done very quickly, others take time.

And i would highly recommend getting them spayed and neutered as the pet overpopulation problem is quite astounding with 4-5 million unwanted pets being put to sleep every year just in shelters alone in the US! That figure does not include all of the euthanasia in vet's offices... You can check with you local humane society or ASPCA to see if they have special funding for the surgery, otherwise when the kittens are 6 months they can start mating, and she can go into heat again right away and you will have hundreds of cats before you know it...
He can be neutered now-always a good idea- to hinder tomcat fighting and hinder potential to mark territory with spraying.
She can be spayed right after surgery.
When the kittens are of age they all should have the surgery, too,
best,
Shanti