Hotel Tango your experience is interesting. In direct contrast, my son (then aged 4) was randomly selected at a UK airport (I think Heathrow) and the guy doing the pat down was emphatic that I stand and observe (it hadn't occurred to me to pay particular attention - perhaps I'm just too trusting!).
Actually, though, that must be the sensible approach - both from the point of view of protecting the child, and preventing any unfounded allegations being made against the security guy at a later date.