On the flip side, and just for "technical" aspect of your question, you could be asking if you could run this as a "hobby"
The IRS has specific rules for running something as a hobby .. read here
Is Your Hobby a For-Profit Endeavor?
BUT
Photography, with clients, creates RISK and liabilities. THIS is a primary concern.
If you run this as a hobby and charge profitable "sessions" then you should cover those Risks and Liabilities as Lew mentions.
But ask a tax adviser for more detailed information.
But from all the horror stories I've heard out there about "newbies" you might want to work on experience first.
If I were to guess, I don't think you even have lighting equipment - flashes, etc etc etc which are really needed for these type of sessions, even if outdoors. Maybe practice on family and friends first if you really want to jump in head first, and then compare your photos to stuff out there from professionals. Don't go by someone saying "oh that looks good". Make yourself your worse critic and remember you only need one client who thinks they can do better than you to bad mouth you all over town. They may have just bought the "pro pack" from Walmart.
I've thought about this venture myself too, and I have alot of the equipment to do it, but I still don't because I know my photography technique, though technically "okay" lacks the composition knowledge and experience. And I lack certain "studio" equipment to do it right.
Don't be discouraged. It sounds like a lot of fun. Maybe do it as fun, and learn, and read, and read, and practice.
Don't put yourself in a position of exposed risks and liabilities right from the get go.