Clinical Outcomes From Treatment and Evaluation of Obstructive Sleep Apnoea in Children With Down Syndrome

The goal of this observational study is to learn about the use of non-invasive ventilation for treatment of obstructive sleep apnoea syndrome in children with Down Syndrome. The main questions it aims to answer are: * What is the impact of non-invasive ventilation on sleep behaviours and quality of life? * What barriers are faced by children and their families in establishing tolerance to non-invasive ventilation? Participants will be asked to complete questionnaires before and after starting treatment. Researchers will compare this data with the results of sleep studies and non-invasive ventilator downloads recorded as part of standard medical care. A sub-group of up to 20 participants will be invited to take part in 45-60 minute interviews exploring expectations, experiences and barriers encountered during non-invasive ventilation therapy.