I didn't do a lot of pediatrics during residency (and none now), but during my short stints dealing with pediatric rehab patients, I noticed an important thing: normal pediatric patients are very difficult to distinguish from brain injury patients. You could probably create a scale that corresponds severity of a brain injury with the age of a kid that the patient acts like.
For example, this was my experience examining an 11 year old boy who we thought might have a traumatic brain injury:
When we were testing his proprioception (which basically means can he tell where parts of his body are in space), we placed a barrier in front of his foot and lifted his toe up or down and having him tell us which way it was pointed. Or as my attending said, "Is your toe pointing towards you or towards the wall?"
The kid was absolutely unable to give a straight answer to this question. Each time (and we did this ad nauseum), he told us everything he could think of that his toe was pointing towards.
Attending: "Is your toe pointing towards you or towards the wall?" (Answer: the wall)
Kid: "Well, it's pointing towards my dad, the wall, that sign, the bathroom, the edge of the bed, and... the door."
Attending: "Is your toe pointing towards you or towards the wall?" (Answer: toward him)
Kid: "Well, that's a trick question because it's really more pointing towards the window, the light, the dresser, my games, and a little towards me."
If an adult answered 10 straight questions in a row like that, I would think that they definitely had a traumatic brain injury. But for an 11 year old kid, we decided it was normal. Annoying, but normal.
And then at some point, the kid took out a robot toy from home that fired little pellets at the wall. I was so relieved when he ran out of pellets, but then he reloaded it. All I could think was, thank god I have a girl.