Is it O.K. to keep the mama rat and the baby rat in the same cage? Or will they fight?

Answers:
Yes, its ok to keep the mom and babies in the same cage, though give mom her space. If she feels threatened or if a baby is sick, she may cannibalize one of the babies (firsthand experience). Research when the babies are old enough to breed, as you'll want to remove the males (males get stinky anyway, I prefer keeping females).
As far as fighting is concerned, they'll eventually establish dominance, wrestling and doing some aggressive grooming, but it shouldn't be anything to worry about. This is actually the best scenerio because the babies are her's, I'm assuming. There'll be no "getting used to" period.
As for rats and rat questions, check this site out: http://www.ratfanclub.org/. The Rat Lady is EXTREMELY helpful and she's got some great info links on her site, even rat first aid.

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You are suppose too keep the mama and babies in the same cage.

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They should be OK together for now. If the baby is a male tho when the baby starts to mature they will mate and then you start a whole generation of inbred rats...

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if you are keeping mommy and a female baby together she will accept her alot easier than she would a strange female.

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As long as they are of the same sex, they should be fine.

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Rats are much happier if they have company. The babies should stay with mom til they're 4 weeks old %26 you can leave the girls with her permanantly as long as you have a big enough cage. Boys are able to mate as young as 5 or 6 weeks so they should be removed to their own space by then. We let our mama rat hang out with her daughters all her life %26 she not only appreciated their companionsip, she *learned* from them-- she was very scared %26 unsocialized when we adopted her, but when she saw how much fun her kids had jumping on people's shoulders, being petted etc. she slowly became more %26 more trusting. Poor girl was even afraid to use her hammock until she saw the little ones playing %26 napping there.

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no sorry the mama will eat it