Tools you should use: Kocher criteria for septic arthritis of the hip
You definitely need to know how to apply the Kocher criteria to differentiate the septic hip from transient synovitis. There's a great online tool at MD Calc for just that.
Tools you should use: Bili Tool
You should use the Bili Tool when assessing a jaundiced newborn in the ED. That's all.
Tools you should use: PECARN Pediatric Head Injury/Trauma Algorithm
I think it's amazing that the Pediatric Emergency Care Applied Research Network has been turned into a verb. As in, "I PEACARN'ed that kid with the head injury and we don't need a CT." This is one of the most widely used tools in our arsenal when caring for injured children in the ED.