Background: A majority of youth who need anxiety treatment never access support. This disparity reflects a need for more accessible, scalable interventions—particularly those that may prevent anxiety in high-risk children, mitigating future need for higher-intensity care. Self- guided single-session interventions (SSIs) may offer a promising path toward this goal, given their demonstrated clinical utility, potential for disseminability, and low-cost. However, existing self-guided SSIs have been designed for completion by adolescents already experiencing symptoms, and their potential for preventing anxiety in children—for instance, by mitigating known anxiety risk factors—remains unexplored. Methods: This trial evaluated the acceptability and proximal effects of Project BRAVE: a web-based, self-guided SSI designed to reduce parent accommodation, a parenting behavior known to increase anxiety risk in offspring. 301 parents reporting elevated anxiety symptoms (98.01% mothers) with children ages 4-10 received either Project BRAVE or an informational control (containing psychoeducational materials and resources); parents self-reported their accommodation of child anxiety and overall distress tolerance at baseline and 2-week follow-up. Results: Relative to control-group parents, parents who received Project BRAVE reported significant reductions in their accommodation of child anxiety (𝑑𝑠=0.61, p<.001), as well as significant increases in their distress tolerance(𝑑𝑠=0.43, p<.001), from baseline to 2-week follow-up. Additionally, parents who completed Project BRAVE rated it as highly acceptable (e.g., easy to use, helpful, engaging) per pre-registered benchmarks. Conclusions: Project BRAVE is an acceptable self-guided SSI for parents of children at-risk for anxiety, yielding proximal reductions in clinically-relevant targets.