Israel arrests up to 700 Palestinian children each year. Up to 94% (of these) are held in pretrial detention without bail.
The graphic is from the Institute for Middle East Understanding. Further information on the issue of children being arrested is provided in an article from the British newspaper, The Guardian. The lead paragraph of the article says:
A belief that every Palestinian child is a potential terrorist may be leading to a "spiral of injustice" and breaches of international law in Israel's treatment of child detainees in military custody, a delegation of eminent British lawyers has concluded in an independent report backed by the Foreign Office.Mondoweiss' Annie Robbins goes into great detail on this issue, revealing that the United Kingdom is taking action against Israel over it.