By Alasdair Glennie PUBLISHED: 16:39 EST, 3 October 2013 | UPDATED: 03:28 EST, 4 October 2013 A rising number of children are using portable tablet computers to access the internet without adult supervision, say experts. The use of handheld devices such as iPads by under-15s tripled in the past year, sparking fears they are able to bypass parental safety filters by using public wireless networks.