Expose the actual wound area and see how deep the damage goes - even the most superficial of wounds can bleed at what appears to be alarming pace, so it may not be as bad as it appears. Once you know just what sort of wound you have it will be easier to advise on the proper course of treatment.
I can see done skin coming off, but not any bone. We have just put him/her under its mum now to keep it warn. Should we put a bandage or anything on it? Will it be ok?
I would not place the chick in with any other birds with a wound of that significance - any bird, mum included, will pick at it and make it worse. If you think about it for a moment, this is how the injury came to be in the first place. You will want/need to brood this bird in a secure setting where it is not at risk of further damage from any other bird.
I would thoroughly clean the wound and go from there depending on what I saw (a picture once you have cleaned the wound would help)
my wiener dog got smacked in the face by one of my 2/3 week old chicks so he promptly ripped the wing off of the chick. all i had at THAT time was some triple antibiotic salve that i used on my cuts etc. i smeared that on the very small part of wing that was left on the chick. i then applied a lot of medicated talcum powder, then gauze with tape on the "stub" and around the chick so the gauze wouldn't come off. i left it alone for 3 days then cut the tape and most of the gauze off. some of the gauze had become part of the scab so i left that bit on there. i made a chicken wire separator in the chicks warming box because the other chicks might peck at the wound(some blood seeped through the gauze). 2 and a half years later and "Lefty" is my best layer.
years ago i had a chicken that been attacked by a coyote. left with a quarter sized hole in her neck that i could swear air was coming from. i spayed a product called "Furox" that i used for my horses wounds, over the hole in the chickens neck until it was caked on very thick. that little hen lived and laid for many many years after BUTT did have a yellow stain on her neck feathers for over a year.
chickens are pretty tough when given a chance to heal up.
Thanks for the information! Today its all dried up and is starting to scab over. She/he is separated from all the others now and I don't think any treatment is needed which is good!