Congrats OP!

What great news!!!!!!!!
I don't know how your employer will take this. It's a toss up at this point. Some may let you bring your new baby to work, others will not be okay w/you bringing along an extra child, etc. You will need to address this w/your boss, but since you really need the income right now, I strongly advise you to not say anything quite yet just in case.
I wouldn't disclose your condition until a month or so. Keep in mind they probably will keep you on for the duration of your pregnancy, but could let you go after you have the baby. I hope they do not, but be prepared for anything.
Good luck.