Obstructive sleep apnoea is a condition which affects an estimated 50% of children with Down syndrome, particularly in their early years. It can cause serious sequelae in affected children but may not be recognised by parents or health professionals. Routine screening has been recommended in some countries but is not standard practice. There are no validated questionnaire based tools available to screen this population of children for this particular sleep-related disorder. Using existing validated sleep questionnaire items, we have developed a questionnaire to screen children with Down syndrome up to 6 years of age for obstructive sleep apnoea, which corresponds with the recommendations made in UK national guidelines. This paper describes these first steps in demonstrating content validity for a new questionnaire which will be subject to further in-depth psychometric analysis. Relevance, clarity and age-appropriateness was rated for 33 items using a content review questionnaire by a group of 18 health professionals with expertise in respiratory paediatrics, neurodevelopmental paediatrics and sleep physiology. The content validity index was calculated for individual items and contributed to decisions about item inclusion. Scale level content validity index for the modified questionnaire of 14 items was at an accepted level of 0.78. Two parents of children with Down syndrome took part in cognitive interviews after completing the modified questionnaire. We describe the development of this 14 item questionnaire to screen for OSA in children with DS from infancy to 6 years.