Objective To explore the authentic experiences of family caregivers of children with osteosarcoma during the treatment decision-making process, aiming to provide a reference for optimizing clinical decision-support services and enhancing caregivers′ decision-making capacity.Methods A phenomenological study design was adopted. Purposive sampling was used to select 13 primary family caregivers of children with osteosarcoma for semi-structured interviews regarding their lived experiences during the treatment process. Data were analyzed and themes were extracted using the Colaizzi seven-step analysis method. Results Three main themes and nine sub-themes were identified:the stage-based evolution of decision-making psychological burden (the shock of the initial diagnosis, decision fatigue during the treatment process, and despair and final choices when facing recurrence); lack of sufficient decision-making time (objective urgency of the disease and treatment milestones, time dilemmas in information acquisition and comprehension, and time dilemmas in coordinating family opinions); urgent need for systemic decision support (demand for visualized information, desire for in-depth communication with the medical team, and expectations for decision-support personnel). Conclusion Family caregivers of children with osteosarcoma face challenges such as psychological pressure that evolves with treatment stages, as well as insufficient decision-making time and support. Healthcare professionals should pay close attention to their stage-specific psychological changes, optimize the timing of decision-making processes, and enhance their decision-making capacity through institutionalized communication channels.