I wish I had seen this topic before, oh well.
First I want to put out a disclaimer, as I have seen "legallady' and others do before. This is not legal advice. These will only be suggestions.
If I were you the first thing I would do is contact your states labor commission and ascertain exactly what the rules are for 14 year old workers. In some states there are special rules for kids who work in restaurants. You can either do it on line, or better yet contact them by phone, email or by letter. Whom ever you correspond with get their name and department for your records and for any follow up communications, and your protection. Try to get everything in writing.
Next, and I hate to do this to you, but as a small business owner, and as a department head I have found this invaluable. You might want to consider deveolping a policy and procedure statement. This would/or could include all the rules and regulations and expectations of the business and of your employees. If you want to be real touchy feely do it with your employees input. Essentially you would want to put out all the terms and conditions of employment, and the positive and negative consequences of following, or not, as the case may be of following the terms and conditions of the policy and procedures statement. This may go a longway in helping you establish the parameters of who and who is not the boss.
With that done, you now have a written document of what the rules are.
With that in place it makes it easier to identify who is not on board with the rules and regulations.
Then you have staff meeting, go over all the elements of the policy and procedures manual, have everyone that they understand the policies and procedures, keep the originals for your business, and give each employee a copy.
Now it is essential that you document in writting when employess do not the p and p manual. Again you keep the original and they get a copy. You have a sh** stirrer in your midst, who may or may not know their employee rights. But if you document legitimate violations, and mete out appropriate discipline, and give them appropriate ways to improve or correct their behavior, remeber do it all in writting, with copies to all involved, then you will have a much better handle on the situation, and perhaps a better case in a wrongful dismissal case.
Sorry this was so long.
OOps forgot, any meetings you have with staff, that are not within the normal working hours makesure you pay them for it. I would suggest that all meetings be held in non-working hours. This is another PC concern which I hate, but it gives the employees a sense of "ownership" to the process.