I'm a refferee at my local field
$10 seems kind of cheap but it really depends on the area and $25 for a party group doesn't make any sense. Your looking to make a profit off this.
Lunch is always great and you can make money of it, try grilling hot dogs or something.
have a stageing area and have field rules posted everywhere.
be familiar with the commonly band paint, i.e. monster ball
A microphone or loud speaker is great for getting everyone ready for the next game in the stageing area.
As for kids being reffs, the deal with that is that they are volunteers, at my field t least, and they get free entry, paint, and air. As long as they have a good manager watching them, they'll be fine.
also:
-about rental equipment?
-what are you going to do about air refills?
-about paint?
-about insurance?