firstly you have to check for danger - is there anything that is likely to cause you to have an accident? once you are sure it is safe you have to assess the child - are they concious, breathing etc.
next check the cut for any foreign objects - do this visually do not poke around with a finger - if you are not a first aider you should send for someone who is and they can then correctly bandage the wound. if no other adult is around send two children with clear simple instructions - tell them who you want by name, and tell them to say a child is hurt - other staff should then come and take the rest of the children away. a decision will be made by the first aider as to whether or not the child needs to be taken to hospital - your manager or a nominated official will contact the child's parents. you need to make sure you record everything that happened including what action you took and who ever helped you in the accident book.
hope this helps.