Two groups of patients will be constituted according to their age; "Group 1" children aged from 3 to 6 years (n = 20) and "Group 2" children aged from 7 to 12 years (n = 20). Within each group, subjects will be randomized to receive either oxytocin or placebo for 12 consecutive weeks. A second period of 12 consecutive oxytocin treatment weeks will then be performed for all patients, followed by a 4-week observation period to document effects after discontinuation of treatment.