Manchester (United Kingdom) - The Manchester terror attack - in which a suicide bomber killed 22 and injured more than 100 at an Ariana Grande concert - has been among the most ruthless attacks due to the victims' ages. Up until Monday's bombing, radical Islamic terrorists have avoided targeting children. But ISIS, which claimed responsibility for the suicide bombing, has seemingly decided to break the long-standing moratorium on directly targeting innocent children. "I don't think anything is off the table anymore," Fred Burton, former special agent and vice president of intelligence at Geopolitical Research Firm Stratfor told Fox News. "We have reached a new low." Other terror experts say that ISIS and other radical Islamic groups have a frequently expressed rationale for targeting Western youth.