My kids 9 and 5 just bumped heads and the 9 year old is vomiting .should i go to the hospital ?

What else ?: It is not unusual for a kid to vomit or get a migraine equivalent headache after even minor head trauma. It would usually be brief & settle with ice chips or other simple rx. If the kid passed out at the time of injury, had a change of personality or memory loss, or vomiting is continuous over time it would indicate a need for further study. If you mom intuition is going bonkers. go in.