When i let my cousins (9 and 12 year olds) play with my R/C I expect there to be broken parts. It goes with the territory... its the nature of the beast. In my opinion, for you to lend a group of 19 year old kids a bunch of R/C cars and not expect broken parts is a bit unrealistic. I know it sucks, but its just the hard reality. They don't have any respect for the R/C because they see them as "toys" to play with, and probably don't know the time and effort you put into building/maintaining them. 100 bucks damage is not too bad, consider it an entertainment expense. You were entertaining your guests. What does a box of fireworks cost? Probably more than 100 bucks for a decent amount.