like 2 hours for an adult, so maybe right before they fall asleep at night will work. ice takes the pain down a lot and can really help.
also, ice on the knee will help a lot, right away, sit with your whole leg resting on a couch or bed, small soft pillow under your knee, ice on knee. as often as you can for pain.
the other neck pain relief technique that really works is the towel technique. you roll up a bath towel long ways like a scarf. put it around your neck so it supports your head, this takes the pressure out of your neck muscles and will reduce 