Head trauma can cause bleeding within the skull cavity. This is of two types. These are intracerebral ( within the brain) and subdural (between the covering of the brain, the dura, and the brain itself). This is the most common type of bleeding that can occur. These two injuries as well as what is commonly called a concussion may all have similar symptoms. The patient needs to be observed for change in neurological status. As a parent, watching for nausea, vomiting, severe headache, slurrded speech, change in mentation, and inability to arouse from sleep are of concern. Most bleeding episodes will poroduce significant changes within 24 hours. However, a slow leak in a subdural ( which occurs because moving ones head shakes the tiny blood vessels between the brain and the dura, can take weeks to develop symptoms. As I recall, President Reagan took several weeks after being thrown from a horse to develop symptoms.
There are good medical studies which show that obtaining skull xrays in patients without neurological symptoms is useless. So, going to the ER for xray without any of the above signs is not indicated. Wake your child every two hours. Confirm that they can recognize you, speak properly, and move all extremities. By the next day should be fine.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.