I'm sorry, but I have to disagree with some of you.
Mentioning returning to the work force after being a stay at home mom, ESPECIALLY on a cover letter, is a terrible idea.
I work in HR and I'm sorry that it's true, but when an employer sees that, first thing, on a cover letter, they're thinking this person is likely new to juggling daycare and a job and perhaps doesn't have a back up plan if the kids get sick......
When I divorced, I'd been out of the work force for 10 years. My resume only mentioned the firms I had previously worked for and the skills that made me valuable. My cover letter explained the reasons I was the best candidate for the position based on my skills and the asset I would be to the company I was applying for due to my relevant experience.
You want to keep things very businesslike. That's what employers and HR managers look at. You don't need to disclose anything further than that until and unless you are asked during an interview. Getting the interview is the important thing.
When I had my first interview after my divorce, I explained the time gap by saying that I was married and my husband's company transferred him quite a bit. My youngest child was starting kindergarten and I was ready and eager to get back into the business world.
I landed the job.
I mentioned absolutely nothing about being divorced, I mentioned nothing about feeling being a stay at home mother was important for my kids. I kept it short and simple.
Being a stay at home mom is a job and it's admirable, but unless you are trying to get a job that requires experience being around kids, it really has no place on a cover letter or resume. Even when asked in an interview, there is no reason to go into details other than to say that you can be available to work as the position requires and you are the best person for the job.
You have to sell yourself.
I've been divorced 15 years and supported two kids by myself. I've left jobs for an even better one. Getting your foot in the door is the first step. You may land the perfect job. You may stay there awhile and gain the experience to add to your resume while looking for a better job.
Keeping the personal stuff out is always the best policy.
That's just my professional opinion.
Best wishes!