You can make money online as a stay at home mom by selling on Amazon, Ebay, or creating a website and blog about something you're passionate about.
If you know a lot about a subject you can write a blog with helpful articles and then Monetize your blog using Adsense, or media.net or sell affiliate products or services.
You can even get work at home jobs and write online for people in your spare time.
Also try writing for hubpages and you can earn money from hubpages articles you write.