While there's nothing wrong with a parent staying home, the assumption I'm seeing in several comments that it's automatically going to be the mother (why don't you stay home, guys? Oh, because you like your job and find your work satisfying? Because you earn a dollar to the female 73 cents and your male-dominated field pays more? Yeesh. Betty Friedan is rolling over in her grave.) is incredibly frustrating. "Plain housewife," please. I work full-time, and let me tell you, it's a lot easier in some ways than full-time childcare. There's nothing plain about it.

That said, the answer to your question, Merlin, is that you and your partner will have to collectively do less of the things you currently do. Prioritize. Pay other people to do things if you can. Drop commitments that have lower effort-to-gain ratios. If your partner chooses to stay home/work part time to make this happen, that's one option. Another is you giving up your career/working part time and staying home. Another is daycare and sitters, and/or giving up or cutting back on social life, hobbies, travel, promotion, outside projects, or the thoroughness with which you do certain things. While you can do everything you did before kidlet post-kidlet, much to my delight, you do it perhaps less often, or not as long/well, or differently. (This applies only to one child - I hear that adding more changes the equation further.)

Paradoxically, you may also be able to do more, in the aggregate. I have become a much more efficient and organized person since becoming a mother, out of necessity. I have, as I said, had to let go of some things, and still let about the same amount of crap fall through the cracks, but the volume of sheer stuff I am able to handle, between kid, home, work, freelance work, social life, and other obligations, is much higher than it once was. Part of this may be biological/habitual - this study suggests that motherhood (and possibly involved fatherhood) may have lasting mental benefits. Part of it is likely just that the presence of a small person in my life demands that I stick to a much more regular routine, which in turn helps keep me consistently organized and high-functioning.

Also know that the childcare ratios will have to shift and remain fluid over time - obviously, a mother who is breastfeeding or can get maternity leave ends up doing a LOT more of the parenting on the front end than a non-lactating parent who can't get a commensurate amount of leave, but don't assume that the amount of time and space you have initially will hold - toddlers are a different kind of work, one that is much less mom-specific, and if you and your partner are both working, the ebb and flow of your jobs will also have to be carefully coordinated with one another to avoid logjams. I have rarely felt such despair as I have the past two years around this time, when my partner and I have both hit work crunches at the same time, while still having to manage everything that goes with taking care of our kid. In other words, we can give you all the advice you like, but the dance of balancing work, personal life, and child(ren) is going to be one that has to be constantly re-thought and reworked as you go on.