The hypothesis of this study is that ultrasound measurements may improve the preoperative detection of difficult laryngoscopy (DL) in pediatrics. The primary objective of this study will be to evaluate the usefulness for the prediction of a DL of five ultrasound measurements obtained from the neck skin to three structures of the upper airway (hyoid, epiglottis and anterior commissure of the vocal cords). Secondary objectives will include establishing, if possible, a cut-off point in these measurements; to compare these measures against the classic pre-intubation clinical screening tests.