Surveillance and screening of child development are crucial to identify delays and promote early interventions, ensuring the healthy development in children. The growing availability of m-health technologies offers new possibilities for these processes. The doctoral study titled Infant and Developing Child Monitoring Questionnaire (ABCD): content validity and feasibility addresses these issues by investigating the theoretical construction and practical implementation of a new screening tool. Objectives of the studies: (1) Investigate the theoretical foundations for the constructing multidimensional instruments for surveillance, screening and diagnosis of child development delay, verifying the most prevalent theoretical model and contrasting it with the biopsychosocial model; (2) Present the construction process and preliminary content validity of the Infant and Developing Child Monitoring Questionnaire (ABCD), aiming to monitor and screen for developmental delays in children aged 2 months to 5 years; (3) Describe the construction stages and content validity of the questionnaire and evaluate development and feasibility of the software; (4) Assess the initial feasibility evidence of the ABCD questionnaire. Methodology: (1) A literature review was conducted using the Medline, Lilacs and Scielo databases, following PRISMA recommendations. Twenty instruments were selected and categorized into six theoretical models: maturational, cognitive, behavioral, neurological, neuropsychological and biopsychosocial; (2) Data collection involved 19 specialist professionals and four stages: bibliographic review, judge analysis, semantic adaptation. The initial pool of 2906 items were reduced to 1198 for future studies; (3): Forty professionals from education, health and technology participated. Stages included literature review, item analysis by judges, semantic adaptation by specialists, user needs identification, solution design, prototype construction, and testing. (4) Data collection was conducted with 179 caregivers of children aged 2 months to 5 years old, both remotely and in-person in 2023 and 2024. Participants had access to the internet and smartphones; Results: (1) The maturational model was the most prevalent and compatible with the biopsychosocial model, underscoring the need for theoretical innovation; (2): The ABCD questionnaire demonstrated preliminary evidence of content validity with promising potential as a mobile app for monitoring child development in Brazil; (3) The ABCD scale in web-app format provided evidence of content validity and feasibility, recommending the integration of the design thinking methodology in the development of m-health tools; (4) The m-health format tool was highly accepted, with 82 percent of participants rating the experience as satisfactory or very satisfactory. Positive indicators of demand, implementation, practicality, adaptation, integration, expansion and limited effectiveness were observed. Conclusion: The studies highlight the importance of solid theoretical foundations and innovation in creating instruments for child development screening. The ABCD web-app emerges as promising tool with high acceptance and practical feasibility. Utilizing m-health technologies can be an effective approach to enhance monitoring of child development, especially in developing countries.