I cannot envisage a terrorist attaching him/ herself to a family travelling on holiday! So although the checks were inadequate, one has to think of the profile of an unarmed terrorist. And it is not that of a young child.
Think again about what you say .. i was in afghan last year and there was two bombings carried out .. one was a 11 year old boy and the other was a 9 year old girl ... made my heart skip a beat when i heard the news of the 11 year old at manchester