I don't doubt that Hamas have vowed to avenge these attacks, but I think it must have taken a fairly hysterical writer to get this:
a top Hamas leader broke cover to warn Israel that the Islamists would kill Jewish children anywhere in the world in revenge for their own young who have died in the devastating assault.
From this, even before you consider what's been lost in translation from Arabic, which is IMO, a very hyberbolic language:
“They have legitimised the murder of their own children by killing the children of Palestine,” said Mahmoud Zahar, in a televised broadcast recorded at a secret location. “They have legitimised the killing of their people all over the world by killing our people.”