How can I treat a head injury that had minor bleeding, is it safe to wash with hydrogen peroxide? Or what is recommended? Is it safe to shampoo?

No peroxide. If this is just a bump that. Bled a little no peroxide shampoo ok biggest problem may be surrounding hair if it needed sutures gental cleaning ok no peroxide if hair a problem might need to shave a small bald spot to hold a dressing dressing a scalp wound in hair is hard. I would be happy to discuss further.
Hydrogen Peroxide. I use hydrogen peroxide only rarely and recommend to my patients to avoid it altogether. Simple lacerations (bleeding stops with pressure after a few minutes) need only clean water and soap as first aid. Of course a head injury must be checked out by a clinician if possible, but as far as hydrogen peroxide, it is toxic to cells and induces cell death. Its best to avoid it.