Zoledronate for Osteopenia in Pediatric Crohn's

* This study is recruiting 40 children and adolescents, aged 6 to 18, who have a proven abnormal bone density as measured on a special type of x-ray called a DEXA-scan. * Participants are allocated at random to one of two groups: either treatment with zoledronate, or a placebo. * Neither the participants or the physicians are aware of which group each participant is in. * Participants are followed every three months for one year, and assessed with blood tests, urine tests, physical examination, diet questionnaire and exercise questionnaire. * Participants have a repeat DEXA scan at 6 and 12 months after beginning the study. * Once all participants are enrolled and followed for one whole year, we will compare the bone density of the group treated with zoledronate with the group treated with placebo.