There are multiple cases of kids getting shut down for operating lemonade stands without business license.
Example... The law is the law and technically you can get in trouble for not registering your business.
Here is the good news. It is not expensive at all to register your business with the state.
Click Here to get started. You don't have to go through the expense of setting up an LLC if you don't want to. It is advisable that you do that (also not very expensive) just for the simple fact that if you are detailing someone's car and something bad happens then you won't lose your house or anything not tied to your business. If you want you can just register as a DBA (doing business as) and put it under your own name. Nothing easier than registering your business with the state. :bigups