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Background: Exposure to arsenic (As) and its metabolites can affect normal growth in children, but the combine effects at simultaneous low-level exposures, remain uncertain. Hence, this study aims to analyze how the combined effects of As and its metabolites can impact growth indicators in 1,792 US children aged 6–12 years, from the NHANES. Methods: Levels of arsenic species in urine were measured using HPLC coupled with ICP-DRC-MS during the 2007–2020 NHANES cycles. The sum of iAs ([AsIII + AsV]), MMA, and DMA was used as a biomarker of internal iAs exposure (∑As), and methylation efficiency was assessed using the primary and secondary methylation indices (PMI, SMI). Linear regression and BKMR models were applied to identify adverse effects, nonlinear associations, interactions, and combined effects. Results: Median concentrations of MMA, DMA, iAs, and ∑As were 0.56 μg/L, 4.07 μg/L, 1.33 μg/L, and 6.40 μg/L, respectively. In the linear regression analyses, higher urinary concentrations of MMA were associated with reductions in several growth indicators. Specifically, each interquartile range (IQR) increase in MMA concentration was linked to decreases of −0.18 (95 % CI: −0.29, −0.06) in Body Mass Index (BMI) Z-score, −0.18 (95 % CI: −0.29, −0.06) in Weight Z-score, and −0.01 (95 % CI: −0.02, −0.01) in Waist circumference/Height ratio. Additionally, higher DMA concentrations were negatively associated with Height Z-score, with a reduction of −0.08 (95 % CI: −0.15, −0.01). In the BKMR analysis, DMA consistently emerged as the dominant contributor across multiple outcomes, showing the highest Posterior Inclusion Probabilities (PIPs) for indicators such as BMI Z-score and Waist circumference/Height ratio. While MMA exhibited notable PIPs in certain models, its influence was generally weaker than that of DMA. Conclusion: Childhood exposure to a mixture of arsenic species, even at low levels, appears to influence growth indicators and adversely affect physical development in children enrolled in NHANES.