So here's a sample pitch to try:
Your name
Your address
Today's date
Leave several blank lines of white space
Dear Mr Bloggs,
I am excited by the opportunity to submit my resume to you for consideration. The position I wish to apply for is (insert name of position and position number if relevant), as advertised in / on (insert name of newspaper or website where you found the advertisement, along with the date of publication).
As a stay at home mom returning to the workforce, I feel I can offer a great deal to your company. Whilst I have not had recent work experience, I have ensured that my skills have remained up to date. I have attended training sessions in (insert name of some training you have done in recent years), and would be extremely keen to continue to develop my skills in this area. I am a competent user of digital technologies, and am able to operate systems and programs such as Word, Excel, Outlook and Photoshop (insert names of other or different computer programs as relevant to your situation).
Some employers are reluctant to offer positions to those who have been out of the workforce for awhile, but I am encouraged by your company's positive attitude and ability to see the future benefits of employing people in my situation. I can assure you that my own positive approach to life and work, together with my ability to quickly master new skills and my desire to reach my goals will be a good match for your company.
I would appreciate the opportunity to discuss my application further with you once you have considered my attached resume. I can be contacted on (insert phone number) to arrange an interview time.
Yours sincerely (if you know the name of the person, or yours faithfully if you don't),
Leave white space above and below your signature
Type your full name and sign above it.