Background: Health Care Professionals struggle to initiate conversations about overweight in toddlerhood. A novel 3D body size scale (3D BSS) may facilitate engagement with this topic during pediatric appointments. Objectives: To explore barriers and facilitators to using the 3D BSS through a mixed-methods design. Methods: For the qualitative phase, parents of toddlers (n = 38) participated in semi-structured interviews introducing the 3D BSS of 4–5-year-old children. For the quantitative phase, pre- and post-interview questionnaires were administered to ascertain the acceptability of the 3D BSS. Results: Parents rated the 3D BSS as “very” (n = 20, 52.6%) to “moderately” (n = 12, 31.6%) acceptable. Thematic analysis revealed four barriers to acceptability: i) the sensitive nature of child weight, ii) the belief that weight does not determine health, iii) the visual normalisation of overweight and iv) the need to account for individual variation in growth patterns. However, these barriers could be overcome through three facilitators: i) the provision of expert guidance ii) the value of simple tools, and iii) tailoring conversations to familial needs. Conclusions: Parents considered the 3D BSS an acceptable visual resource to discuss child weight during routine appointments. However, the acceptability of the tool was conditional on a sensitive, collaborative, and tailored delivery approach.