how can cellphones be used to do a crime against children?

im writing up a report about banning cellphones for the kids under the age of 13, and it would help me a lot if you guys give me a headsup. am i using the word headsup correctly? anyway, i was thinking of putting something like "1 click crime", but that wouldnt be enough, is it? i already put bullying in my 1st paragraph.