the indentation there may be a bony one and in my opinion you should go to ER for re-evaluation. if the child is asymptomatic may be nothing would be needed but it is important to know the extension of the indentation, if its there, to be safe.
this may need CAT scan of head to be done to asses the injury
generally if its not pressing on any intracranial soft tissue
(structures inside the skull) no intervention is needed. and i think that would be the case with your child as he is free of any symptoms.
you have to be vigilant of any danger signs that ve been explained to you.
in some cases the these kind of injuries may manifest even after months even, so you have to keep this mind too.
wish your child a rapid recovery
Dr. Amit Kumar