Beware the limping kiddie. Non-weight bearing kids have septic arthritis, a potentially high-complication disease, high up on the differential. Here is some info on the Kocher criteria that has been validated. Also here is a GREAT presentation on determining the etiology of a limp, particularly septic arthritis vs transient or toxic synovitis.
Kocher criteria for a child with a painful hip, suspected to have septic arthritis:
1) non-weight-bearing on affect side
2) sedimentation rate greater than 40 mm/hr
4) WBC >12,000
Criteria met and probability child has septic arthritis
4/4 -- 99%
3/4 -- 93%
2/4 -- 40%
1/4 -- 3%
Kocher etal. Validation of a Clinical Prediction Rule for the Differentiation Between Septic Arthritis and Transient Synovitis of the Hip in Children. The Journal of Bone and Joint Surgery (American) 86:1629-1635 (2004).