They were in a refugee camp in Turkey but had been issued visas for Canada, as the mother's sister had satisfied the Canadian government's requirements.
However the Turks wouldn't issue them an exit visa or otherwise process the necessary paperwork. So they were trying to get to Greece in order that they could journey on to Canada. And as someone else said, the Turks could quite easily have forced them back into Syria and may have been planning to do so. I don't think I'd want to take that chance.
Similar things happened prior to WWII when Jews trying to flee Germany couldn't get out because the British government wouldn't issue visas unless the German authorities provided exit papers. But the Germans wouldn't provide exit papers unless the British provided visas. So despite having the necessary financial support guaranteed in England, hundreds of thousands were murdered because of wilful bureaucracy.
But it's alright because we took a few hundred kids as a humanitarian gesture, but only one per family. So the few families offered a lifeline had to make a Sophie's Choice decision about which child lived and which would have to face up to whatever fate awaited them (which was almost inevitably a gruesome death).