This document contains the study protocol for the research project assessing the Construct and Concurrent Validity of the Test of Infants' Daily Living Activities (IDLA) against the Alberta Infant Motor Scale (AIMS). The protocol outlines the methodological framework implemented in the study, including: • Study Objectives: Assessment of construct validity (postural and motor control domains) and diagnostic accuracy. • Participants: Inclusion and exclusion criteria for the infant population (1-18 months). • Procedures: The examination protocol using AIMS (reference standard) and IDLA (index test). • Statistical Analysis Plan (SAP): Detailed plan including Spearman’s rank correlation, ROC curve analysis for cut-off point determination (Pareto optimal criterion), and logistic regression models. This protocol details the methodology and analysis plan implemented in accordance with the ethical approval granted by the Thematic Team for Ethics in Scientific Research of Physiotherapists at the Polish Chamber of Physiotherapists (Resolution no. 15/52) on June 29, 2022.