Well I had the same situation. My class was going on a camping trip for 3 days and my parents refused me to go. I told them all the benefits of camping and how much fun I would have. I also told them that there would be supervision and it's a safe environment. Hearing all those things they let me go so you should try it out.
Will there be adult supervision? If, as you say, the field is very close to your house, why not invite your mother to spend some time with the group or have some adults look in on you from time to time. If her only concern is your safety, it would be a good idea. Someone should have a cell phone in case of emergency, and someone should know something about first aid. Have a serious talk with your mom, and give her all the details. I see nothing wrong with a group of 13 year olds camping out close to home, but I also think an adult should be around. Another thing; is this a co-ed group? If so, I understand your mother's concern. The best thing is try to be mature about it even if she won't allow you to participate. If you show her you can act responsibly, she may have a change of heart or permit you to go another time.
Say what the hell you hate me then run away crying and don't talk to them for like 5 days.
I agree with robbier44, if all that is going is a group of 13 year olds with no supervision....my answer would be NO as well. You may think you're all grown up, but believe me you are not. With a group of 10 I would suggest 2 adult supervisors, preferably a husband wife team especially if it is co-ed. Perhaps one or both with training in First Aid. The world isn't the place it used to be. Where one could sleep with their windows open and their doors unlocked. We all have to be extremely safety conscious these days.
Well if thats the matter, tell your parents they don't trust you. Try to tell them everything about the camping trip. Hope this works
Tell them everything about the trip so they know you're not hiding any motives. Tell them how much alcohol and weed will be consumed, how you intend to invite 10 bitches over for an orgy, etc etc...