Daughter hit her head on a metal bar at the park. it instantly had an indent come up. should i be worried?

Closed head injury: Do you mean that there is an indented area on her skull? If so she should be seen. Otherwise, just call your physician, to make sure they don't think she is at risk for concussion.

Keep a close eye: Indentation from a head injury is common and not necessarily a sign of worry in and in itself, esp in young children who have pliable skull bones. More imp. Is to look for other sign of internal head injury causing bleeding such as change in mental alertness, vomiting or headaches. These symptoms can develop anytime in first 3 days for which the child would need to be seen at the hospital quickly