I agree with some others on here, very sad for your children, but what would you do if you hit a cat at night 'without a collar'? Expecting the driver to pick the animal up, internet search a 24hr vet, take it there, pay the bill and then try to track down the owner is never going to happen. Maybe this link clarifies the situation: http://www.bbc.co.uk/news/uk-england-gloucestershire-15457756