Seeing as how a father ended up dead, yes throwing of a rock, is exactly like firing a gun at someone. If the kids took a tank and drive over the car and killed the man, how is it any different, they killed a man because they have no morals. Rock, gun, tank, Drano pick your weapon sane outcome.
Have you taken a look at this little rock you think might only dent the hood, its fucking massive. That "rock" has to weigh 8 pounds.
I'm not sure that id be able to throw that rock at 65 miles an hour at someone, but if I could I would be pretty sure that if it hit his head he would have a pretty small chance of living through it.
If your trying to justify this as some 'boys will be boys' stunt then ya, you have parenting issues. This was not a fight in the schoolyard, theres a difference.