I don't want to burst your bubble.....
While you are cooking the meal as a favor, it could be construed as the same as having guests over for dinner; you wouldn't need a catering license, however I don't think licensing would be your issue of concern.
The issue that would raise a flag is that you are not cooking in your home and inviting guests into your home. You are using another location for (possibly cooking) and serving to a group of people whom you personally did not invite, some may be friends, but also some strangers as well. I think the only way your idea could fly is if you had this picnic style on your property, or possibly on one of the parents property. Check with your local health codes and licensing requirements. More importantly think about what liabilities are you holding yourself open to?
Just keep in mind that someone doesn't actually have to get sick to create a legal issue for you, they only have to claim being ill to rack up your legal bills that you could incur. We live in a litigious society today and sadly those who look to gain an edge are often handsomely rewarded in our courts.
