Dealing with unexpected second mouse litter

Question
I rescued a mama mouse and 5 nursing babies, I didn't think it would be hard to socialize them and after all thats only 6 mice, nothing a nice big tank cant handle right!? WRONG! I checked today (I have had them for 2 weeks now) and mama has 6 NEWBORNS! The others were JUST weaned! I separated all the babies from mama, worried that the 1st litter might stress her out and I don't want her eating her babies. I need to very soon, separate them by sex, can I re-unite the girls with mama after the other babies are a little bigger? I have 2 very large set ups one for the males and one for the females, the new babies complicated the situation a little! it has only been 4 hours since they have been separated, tomorrow morning should I put them all back in one tank together? I am not sure what to do!! Thanks in Advance!!

Answer
Dear Camie,

Mice often mate within a few hours after giving birth.  This is how they have litter after litter, every three weeks!  It was a good idea to separate the mice since the larger babies would push the smaller ones out of the way at nursing time.  You can put all the girls together when you are ready.  The bad news is that boy mice don't always get along.  Eventually there will probably be fighting.  Often a male mouse has to have his own cage for this reason.  It's ok for there to be a lot of squeaking in a mouse cage, but blood means it's time to separate them.  The cages should be as close as possible so they can continue to communicate with each other, as it's rather lonely being a bachelor mouse.  

This site does a great job showing the difference between the mouse sexes:

http://www.thefunmouse.com/info/sexing.cfm

Have fun!

squeaks n giggles,

Natasha