I would hope that someone starting a business would have a better understanding of the craft. Don't take that the wrong way, we all have to start somewhere.
You are not the only one. I understand how nice it is to want to be a pro photographer after some people begin telling you how nice your images are.
Now that you believe you have the right to charge a person for your abilities, ask yourself if you have the three things that the pro's have.
1. They have the correct equipment.
2. They have the experience.
3. They have the knowledge of what it takes to deliver a finished product to the client.
Is your equipment good enough to deliver professional results? A true pro can deliver great images with any acceptable system.
Do you have back up memory cards?
Extra batteries for your camera and flash?
Extra lenses?
Extra camera?
Have you thought about what happens if you can't make it to the shoot?
What do you do if the client is unhappy with the final images?
What happens if your computer crashes during the editing process and you lose all the images?
What if the client gets hurt during the shoot?
What happens if you get hurt during the shoot?
What happens if you can't get the images to the client on time?
What happens if you can't get to the shoot on time?
How are you billing the client?
Do you need a model release?
Do you need a property release?
Do you have a contract? Do you need one?
What do you say to the client if they want the copyright?
What kind of usage agreement do you offer to the client? And for how long?
Are you offering the images on print? On cd? on dvd?
Are you offering full resolution images?
Do you place a watermark on the images?
I am sure that if you have read this far you are starting to get the point. This is not meant to scare you, or keep you from finding paying gigs. It is however a beginning to the questions that you have to ask yourself before making the move to professional photography.
Once you charge, you are professional. (if only for that shoot)
You can be sued, you can have your budding photography career shortened by receiving a bad reputation. Simply because you were not prepared.
If this were easy, everyone would be doing it.
Insurance for your gear is not cheap.
Liability insurance is not cheap.
The correct gear is not cheap.
However, all of these are cheaper than the lawyer who will defend you in a lawsuit.
Keep in mind that in the states, getting money in a lawsuit is far easy than playing the lottery. Also keep in mind that your lawyer will charge you the same rate whether you are right or wrong.
While it is cool that your friend is offering $50 to come out and shoot the kids, the decision has to be based on sound business logic.