On the resume, say nothing. List your professional jobs and don't call attention to the gap in employment. If you absolutley feel the need to do so, you could briefly mention it in your cover letter: Looking forward to re-entering the sales field . . . "
The interviewer won't have much trouble figuring out where you've been: your age will probably be "guessable" within a couple years based upon your graduation dates, and a person with much investigative sense will figure out where you've been. A gap in employment is quite acceptable for a woman -- less so for a man, right or wrong.
I suspect CED is right: you may not even be asked about it; however, you should have some answers ready.
Over-emphasizing having stayed at home is suicide. If your interviewer has always been a working mom, you may insult her if you wax fantastical about the joys of seeing the first steps, the dangers of leaving children at danger, etc. On the other hand, if she was a SAHM herself, or if she wishes she were a SAHM, you risk her wondering whether you're serious about returning to the work world, or whether you'll run back home when you hit a rough patch at work. If you explain it in terms of finances (if I'd worked, I would've only made ___ after day care), well, you look a little pathetic, even if the math is clearly in your favor. It's best to focus on your future as an employee and say as little as possible about having been at home for years.
The interviewer can legally ask you about a gap in your employment, but he or she cannot ask you whether you intend to have more children, whether you have reliable daycare, or whether you're a single mom. On the other hand, he or she CAN ask whether you're available to work late without much notice, whether you're available to travel, etc -- assuming this is part of the job, of course.
If an employer asks you something "questionable", you're in a tough spot. If you refuse to answer, you risk looking uncooperative, and who wants to work with someone like that? On the other hand, if you feel the answer may make you look like a less-than-desirable candidate, you should deflect the question and turn it to something that puts you in a better light. For example, if the interviewer asks if you're ready emotionally to leave your children in daycare, you could reply, "My children have visited the day care and they're excited about starting there, and I'm looking forward to ____ about returning to work with this company . . . " Make the conversation about your future work, not your having stayed at home.