Hi Melissa, it's great to have you here!

I can really relate to your feelings of wanting to be at home with your kids - we don't have any (yet

) but talk often of how lucky we are to be set up with a business that allows us to work from home so that when we DO make the plunge into parenthood we're well prepared to handle both business and baby - or so we hope!
There are so many aspects of being a practicing VA that will come into being for you as you develop your own vision for your business so don't worry that you're starting from 'scratch' - I did too once and all turned out well! It was just a matter of figuring out *what* I wanted to offer and how I would structure that from a business perspective to find clients, further develop my business/skills, and thus further my practice as a VA.
I think in the beginning it can be hard to imagine what it might become, but like anything, it's a matter of investing your heart, time, energy, and vision.
I'd say start out by brainstorming a list of all the services you would like to offer, try seeing if there is a niche there (like, will you focus on working with a certain niche of the business community, or do you specialize in a particular skill or direction that you could market yourself on more heavily than the rest of your admin skills). Don't worry if that's not immediately obvious - just think of all the ways you can help business professionals and small business owners get more work done at the end of the day by taking on projects and deadlines for them from your own home office.
Take some time to figure out how much your time is worth (relative to your skill sets, experience, location, etc.) and then spend a bit of time marketing yourself like never before

(you can do this by setting up a professional website, creating fliers to hang up in the office district of your neighborhood, creating professional profiles on the business-oriented social networking sites - like linkedin, etc.)
There are lots of great topics on the forum here, if you scan the various main forums to view the many threads already started, I think you'll find alot of good info/conversations going on - and of course, feel free to add to any of them at all or start your own with any questions you have as you go along.
As always, the forum is here to offer support and answer questions whenever you run across something that you find you need the help of a community of other professionals on! And that's a great first step, being a part of something devoted to your success as a VA