Its not really surprising, urban foxes are frightened of us in the same way that hyenas are frightened of lions, they'll keep their distance but always be looking for a chance to take a bit of a kill or a cub. Quite scary when you think about it, I have 2 kids aged 2 and 5 months, and although where I live the foxes are country types if I lived in the city I'd think twice about leaving them alone, even in a suburban back garden. IIRC this is the second child to be attacked by a fox...