It is obviously barbaric.
However these group their strength is the publicity they generate. Al Qaeda was never very powerful on its own, the ideas were powerful. I mean accounts of Afgan 1 is they and other precursor groups like Egyptian Jihad, did little actually fighting. But not only did they claim to, they took full credit for winning.
That child is probably going to be damaged for life.
ISIS is heavily funded and from so called allies. In some case they may have been directly armed.