Subbing! Going from one to two children has been insanely hard on us. I wanted four but I'm kind of scared to have any more after this. DH and I are both having second thoughts, actually. DD will be six months in a week or so and I still feel completely overwhelmed. How do you moms-of-many do it? I can't even imagine.
Oh, I so felt the same way when my DS (our #2) was six months! For the first couple of weeks after he was born, I was so besotted with his infant self that I knew I wanted a third. Then reality set in, things got crazy as they do with two kids 2 and under, and for the next 9-12 months I said that not only were we not on a "two with an option for three" plan, but we might well be on a "two with an option for one" plan, and which kid did the person I was talking to want to take home with them?
Then things started to ease up a bit as DS got to be a little over a year. He got less crazy-clingy. He and ODD started learning how to play together. And I started figuring out how to manage the whole routine. So by the time he was 18 months old...I decided we definitely did want one more. Now with YDD, our family just seems absolutely perfect. She completes it in a way that I can't quite explain. And as much as I was conflicted about wanting a third for awhile, I'm not at all conflicted about a fourth--we're done. We're perfect at a family of five.
Anyway, I don't have any brilliant advice about managing three (or even two little ones)...I just muddle through! But I would say that if you're not sure whether or not you want another, don't make any firm decisions until after your youngest is over a year. That first year is so taxing, mentally, emotionally and physically (even though it's also wonderful!) that it's not a good time to be making absolutely final decisions if you feel in any way conflicted.