A warning has been issued to parents that ore children are being drawn into extremism online with youths now accounting for one in five counter terrorism cases. The officer who led the Alfie Coleman terrorist investigation issued the warning after the neo-Nazi was jailed. Detective Chief Superintendent Helen Flanagan called for parents to be more vigilant, saying “horrific” terrorist manifestos and other extreme material are just “one click” away. The head of operations for the Met’s Counter Terrorism Command spoke out about the growing trend as Coleman, now 21, from Essex, was found guilty of planning a mass gun attack. Coleman was thwarted thanks to a joint operation between police and MI5, which deployed undercover operatives to engage Coleman online as he tried to buy automatic weapons. Police swooped in to arrest Coleman moments after he picked up a Makarov handgun and ammunition in a car park in east London.…