Persuasive messages can motivate parent support for physical activity (PA). Many PA messages targeting parents are not necessarily inclusive of parents of children with disabilities (CWD). Guided by the theory of planned behavior and multi-process action control model, the relative effects of PA messages were examined among parents of CWD. Parents (N = 135) were randomized to view one of four PA messages. Parent support for PA and various psychosocial antecedents were assessed before and after message viewing, along with message preference. Baseline parent support for PA acted as a moderator on the effects of messages. Effects of messages did not differ between message conditions. Overall message effects were observed for attitudes, subjective norms and planning. Parent support for PA increased only among parents with low baseline parent support and the inclusive message was most preferred. This study can inform the development of PA messages targeting this population.