Introduction: Hematopoietic stem cell transplantation (HSCT) is a critical treatment for lifethreatening diseases in children, yet post-transplantation complications frequently lead to unplanned readmissions, placing a significant burden on families and healthcare systems. Objective: To investigate the incidence and influencing factors of unplanned readmissions in children undergoing HSCT, and to develop and validate a risk prediction model. Methods: This prospective study enrolled 307 children who underwent HSCT at a tertiary children’s hospital in Chongqing between January 2023 and December 2025. Lasso regression was used for variable selection, and logistic regression identified independent predictors. A nomogram was constructed, and model performance was evaluated using the area under the receiver operating characteristic curve (AUC), Hosmer–Lemeshow test, and ten-fold crossvalidation. Results: The incidence of unplanned readmissions was 23.13% (71/307). Independent predictors included conditioning regimen, STRONGkids score, systemic immune-inflammation index, GAD-2 score, Caregiver Preparedness Scale score, and Family Caregiver Task Inventory score (all P