First, a pro-Israel person will point out the following:
Throwing rocks at cops/soldiers is an aggressive act that one can easily be arrested for. Every country on Earth would arrest (at BEST) children who throw rocks.
Let's take a look at how the anti-Zionists justify the use of child soldiers:
The Jews do it too!
Well, Israel shouldn't exist so it's OK.
Well, Israel can stop the kids, but they are just too mean when they do!
Children can do whatever they want (seriously)
And the all time classic: "It's OK because they are occupied."
For any other group of people, sending children to the front lines to fight soldiers and then complaining when they get arrested would be pathetic and universally condemned. For the Palestinians, it gets them sympathetic front page headlines.