Background Doctors sometimes encounter parents who object to prescribed treatment for their children, and request suboptimal substitutes be administered instead. Previous studies have focused on parental refusal of treatment and when this should be permitted, but the ethics of requests for suboptimal treatment has not been explored. Methods The paper consists of two parts: an empirical analysis and an ethical analysis. We performed an online survey with a sample of the general public to assess respondents’ thresholds for acceptable harm and expense resulting from parental choice, and the role that religion played in their judgement. We also identified and applied existing ethical frameworks to the case described in the survey to compare theoretical and empirical results. Results Two hundred and forty-two Mechanical Turk workers took our survey and there were 178 valid responses. Respondents’ agreement to provide treatment decreased as the risk or cost of the requested substitute increased. More than 50% of participants were prepared to provide treatment that would involve a small absolute increased risk of death for the child and a cost increase of US$<500, respectively. Religiously motivated requests were significantly more likely to be allowed. Existing ethical frameworks largely yielded ambiguous results for the case. There were clear inconsistencies between the theoretical and empirical results. Conclusion Drawing on both survey results and ethical analysis, we propose a potential model and thresholds for deciding about the permissibility of suboptimal treatment requests.