BACKGROUND: Pet ownership brings many health benefits to individuals. In children developmental benefits can extend to improved self-esteem, better social competence and decreased loneliness. The majority of households with children own a dog, however only a small proportion of children gain the benefits of dog ownership through dog walking and play. There are few intervention studies investigating the impact of dog-facilitated physical activity in children. The PLAYCE PAWS study aims to test a minimal-contact intervention through the use of mobile health ("mhealth") strategies, i.e. text (SMS) messages, to parents to encourage their children to walk and play with their dog more, and evaluate the impact on children's overall physical activity and development. METHODS/DESIGN: The PLAYCE PAWS intervention study will target parents in dog-owning families with children aged 5 to 8 years in Perth, Western Australia. Approximately 150 dog-owning parents and children will be randomly allocated into either one of two intervention groups or a 'usual care' control group. The first intervention group will receive SMS messages over 4 weeks to encourage and prompt parents to undertake dog walking and dog play with their child. The second intervention group will receive the same text messages, plus a dog pedometer and personalised 'dog steps' diary for their child to complete. Parent-reported outcome measures include changes in children's dog walking and play, overall physical activity, socio-emotional development, self-regulation, self-esteem, empathy, and level of attachment to their dog. DISCUSSION: The PLAYCE PAWS study appears to be the first to examine the effectiveness of a low-cost, mhealth intervention for increasing young children's physical activity through dog walking and play. Given the high prevalence of dogs as family pets, this study presents a valuable opportunity to investigate if mHealth interventions encourage children to walk and play with their dog more, and if there are any associated impact on children's overall physical activity and socio-emotional well-being. If effective, a larger trial or program could be implemented at low-cost and with wide reach in the community. TRIAL REGISTRATION: ANZCTR, ACTRN12620000288921 . Registered 4th March 2020 - Retrospectively registered.