Try to find a native animal veterinary centre, they treat injured wildlife. Regular vets will feed it and keep it warm, but will put it down if it does not look like it will survive. But a regular vet would be better than no vet at all! They wont charge you to look after a native animal.
I hope the little bird survives but it does not sound like it will work out well. I think its great that you care enough to look after the poor bird though.
And it WILL happen again if you continue to let your cats outside, sadly. Which i know is a dilemma, as they will be upset if they are suddenly not allowed outside. The best option it to keep them indoors at all times. But even if you just bring them indoors for nightime, it will cut down on the amount of animals they will hunt. It's just their nature, they cannot help it :(
Make sure the next cat your family gets stays as an indoor cat. Better for the cat and for the environment. Good luck i hope the bird is ok :)