I would just fill it out with your work experience "as is". Put in a little bit about being a room mom, etc., but don't over-do it. If you do, you risk them thinking that your entire identity is tied up in being a mom, and they may think you'll not be dedicated to your work.
In the cover letter and at the interview you'll have an opportunity to explain that you've been home with your children for years. This is a perfectly acceptable reason for a "hole" in your resume, and it won't be held against you (on the other hand, it's much more difficult for a man to explain a similar absence).
When you're interviewed, you'll want to be ready for the "Whatcha been doing?" question. You can deflect that question though and turn it into a positive for you:
"I chose to stay at home with my children for several years. (one sentence on where you've been -- now details on where you want to go -- this is what you want them to remember) Now they're older and in school, and I'm ready to resume my career. I'm excited about getting back into the work force, and I hope to . . . "
Do not go into WHY you stayed home with your children. It doesn't matter anyway, and if the interviewer is a working mom or the husband of a working mom, you risk alienating yourself if you extole the virtues of staying home with your children, and you risk having them believe that you might go running back home after only a few weeks, leaving them to seek and train someone new. Instead, turn the conversation to THE FUTURE and what you hope to accomplish in your new position. Legally, you don't have to answer questions about your personal life in any way, but if you appear closed-mouthed on the subject, it'll send up red flags to the interviewer -- better to tell a little and be seen as honest and forthcoming.
I think the biggest mistake most people make -- SAHMs or anyone else -- is failing to be aggressive enough at getting your foot in the door. Put in your application (along with your resume and a nice cover letter), and ASK who will be calling you and when you might expect the call. If they fail to call, CALL THEM. At the interview, ASK when a decision will be made; if they don't call, CALL THEM. The day after your interview, put a professional thank-you letter (thanking the interviewer for his/her time and quickly reiterating your interest in the job -- be specific) in the mail to the interviewer. You have nothing to lose by aggressively pursuing the job; you have everything to lose by sitting back and hoping to be noticed.