Muscle and physical activity play an important role in in growth, development and bone health in healthy children, especially during puberty. Children with inflammatory bowel disease (IBD) have lower level and intensity of physical compared to a control group. Several studies have shown that children with IBD have a lower bone mineral density (BMD) than general population, due to risk factors such as corticosteroid use, disease intensity, inflammation, malnutrition and a vitamin D deficiency. This low BMD is associated with an increased risk of fracture. A recent observational study found a positive and significant correlation between BMD in IBD patients and time spent in moderate to vigorous physical activity for one week (unpublished data).The present study aims to show a benefit of an adapted physical activity program on BMD in children and adolescents with IBD.

Inclusion Criteria:

• Patient with IBD (Crohn's disease, ulcerative colitis or unclassified chronic colitis) since at least 6 months.
• Computer and internet access at home.
• Consent to adhere to a physical activity program.
• Assent of the child to participation in the research protocol.
• Informed consent of parents or legal guardian.
• Patient benefiting from national health.

Exclusion Criteria:

• At time of inclusion, acute intercurrent events which may lead to a decrease in physical activity (according to the judgment of the investigator) as fractures, recent arthritis, ano-perineal lesions, severe dermatological lesions.
• Chronic, acute or intermittent diseases (other than IBD) that may lead to a decrease in physical activity.
• Refusal of the child to participate to the protocol.
• Refusal of one of the child's parents to participate in the protocol.
• Predictable lack of compliance to study procedures (especially to the physical activity program).
• Child with visual impairment.
• Participation in another interventional study.
• Pregnant or lactating women.
• Patient under protection of justice.