If your infant has a head injury, even if it is not serious i would suggest you still take your infant to the hospital to be checked. A head injury is nothing to play with and should be taken care of as soon as possible. Make sure that you don't allow the infant to go to sleep until you know they are ok, Its possible they could have a concussion and cause serious issues if not treated.

Did your infant hit there head, If so how hard?

Please get them to the doctor as soon as you can!

Since a infant's head is still developing, any trauma can be life threatening, whether there is any external damage or not. If the child is bleeding, first call 911 and place a cloth over the wound and press with enough pressure to stop or slow the bleed down. If the child shows no outward damage, call 911 and keep your hand under the head so that the baby's head doesn't wobble back and forth. You can fore-go calling 911 if someone is there to drive you to the hospital. In a pinch drive to a local fire station for advanced first aid before calling for an ambulance. Remain calm. Most kids are pretty tough but error on the side of caution and get the child checked out.