This chapter provides insight into the issues associated with researching with children and guidelines for researchers intending to work with this group. When working with children ethics considerations are paramount and their welfare as participants in any research study or project should be upheld at all times. The principles of informed consent should also be adhered to and researchers working with children need to ensure good safeguarding procedures are in place prior to any research study or project commencing. Once a research study has commenced there are then key aspects related to recruitment and retention and study logistics, relating to time, location, transport and cost which need special consideration when working with paediatric populations. The chapter contextualizes and highlights these issues with an example from the topic of physical activity monitoring.