Tris(1-chloro-2-propyl) phosphate (TCIPP) is frequently applied to consumer products as a flame retardant and is commonly detected in indoor environments. Urinary bis(1-chloro-2-propyl) phosphate (BCIPP) is typically measured as TCIPP's primary biomarker but has been inconsistently detected. Bis(2-chloro-isopropyl) hydroxy-isopropyl phosphate (BCIPHIPP) was suggested as an improved biomarker due to its common urinary detection. To evaluate biomarker utility, we compiled individual data from children ages 1 month to 6 years (n = 292) from two cohort studies (2014-2018). Concentrations of BCIPP, BCIPHIPP, their molar sum, and their ratio were examined for association with age and other characteristics. Both biomarkers were detected frequently (>80%); however, metabolite levels and dominant metabolite varied with age. For each month increase in age, the molar sum of metabolites decreased by 4% (10β = 0.96; 95% CI = 0.95-0.98), which was driven by decreasing BCIPP. The BCIPHIPP:BCIPP ratio also increased by 0.10 per month of age (95% CI = 0.08-0.13). Children with a college graduate parent had lower ratios (p = 0.0003) despite no difference in molar sum of metabolites. Metabolism differences and changing exposure pathways during early life may contribute to observed patterns. Cumulatively, results suggest biomonitoring efforts should include BCIPP, BCIPHIPP, and other possible metabolites, since a single biomarker could underestimate total TCIPP exposure.