A bronchoscopic study of anaesthetised infants and children receiving cricoid pressure revealed the procedure to distort the airway or occlude it by more than 50% with as little as 5N of force in under 1s and between 15 and 25N in teenagers. Therefore forces well below the recommended value of 30 N will cause significant compression/distortion of the airway in a child

Effect of cricoid force on airway calibre in children: a bronchoscopic assessment
Br J Anaesth. 2010 Jan;104(1):71-4