Flame retardants (FRs) are chemicals used to reduce the flammability of materials and are commonly found in consumer products such as furniture and electronics. These substances can migrate from products (e.g., furniture foam and electronic devices) into indoor environments such as air and dust and may pose risk to human health by direct exposure. Some FRs are known endocrine disruptors capable of affecting thyroid hormone homeostasis, neurodevelopment, behaviour and reproduction. Thus, there is a need to understand the emission, transport, sorption, and distribution of FRs. In line with the 3R principles (Reduce, Replace and Refine) used in scientific research and risk assessment, modelling has become a valuable tool for elucidating and predicting the emissions, behaviour and fate of semi-volatile organic compounds (SVOCs) in indoor environments. i-SVOC is a software application designed for dynamic modelling of these chemicals covering indoor compartments contributing to a more efficient evaluation of indoor pollution. This study had two main objectives. First, we aimed to develop and validate a model to estimate the concentrations of two FRs, tris(chloroisopropyl)-phosphate (TClPP) and triphenyl phosphate (TPhP) in Spanish indoor environments. Second, we sought to estimate the indoor levels and exposure to both FRs in Spain by modelling environmental data from a toddler Spanish birth cohort (GENEIDA). Four scenarios were simulated using the i-SVOC software, considering variation in ventilation (high/low) and emissions factors (high/medium). This study demonstrated the ability of i-SVOC model to estimate TClPP and TPhP concentrations in air and dust. The application of the model to environmental data from the GENEIDA cohort showed statistically similar mean/median values to those experimentally collected, leading to comparable estimates of FR-exposure. Furthermore, the non-carcinogenic risk from exposure to TClPP and TPhP in toddlers were assessed. However, no correlation was found between the estimated exposure levels and the measured concentrations of FR metabolites (bis(1-chloro-2-propyl) phosphate -BClPP- and diphenyl phosphate -DPhP-) in the cohort toddlers. This discrepancy is likely due to variability in environmental characteristics and individual differences in metabolite concentrations.