You can report it but also have a conference with the principal and the counselor, because now you are involved, the student came to you. It is you the student trust, so it is you that student is depending on to take action. They will want to meet with the student and maybe authorities to ask questions.
Just in case the child wasn't serious, talk to the family. if you suspect there might be problems take it further to the guidance counseillor. The child might have just exaggerated a small hit on the shoulders. based on what you have said thats all i can assume.
Depending on the laws of your state, you probably have a legal obligation to report it. In many states teachers, counselor and medical personnel are required to report allegations of child abuse to the police.
Educators, counselors and medical professionals are required by law to report suspected child abuse in the state of Texas. I don't know about other states, but it's probably similar. Don't depend on someone else to take care of your responsibility. You can report it to the counselor and administration, but it is your obligation to report it. Besides the more people who report it, the better.