same injury in different subject will produce different effects. what is to be done is in all cases of head injury what you need is to observe the child for 24 hours. if every thing is fine than not to worry, if any of the symptom of injury to head like baby becomes drowsy, vomiting, any fits, immideately you need to take the child to ER for the evaulation of the head. watch the baby for 24 to 48 hours at least