This study assessed relationships of duration of family Special Supplemental Nutrition Program for Women, Infants and Children (WIC) participation with racial/ethnic disparities in child sugar-sweetened beverage (SSB) and water intake. Child beverage intake and family duration on WIC were collected during three cross-sectional surveys of WIC-participating families in Los Angeles County, California (2014, 2017 and 2020; n = 11,482). The associations of family duration of WIC participation, a proxy for the amount of WIC services received, with daily intake of total SSBs, fruit-flavored SSBs and water were assessed in race/ethnicity strata with multivariable negative binomial and Poisson regression models. Among English-speaking Hispanic children, those of families reporting 10 years of WIC participation consumed 33% and 27% fewer servings of total and fruit-flavored SSBs compared to those of families reporting 1 year on WIC. Among Black children, those from families reporting 5 and 10 years of participation in WIC consumed 33% and 45% more daily servings of fruit-flavored SSBs than those from families reporting 1 year on WIC. Disparities in daily total and fruit-flavored SSB intake between Black and White children increased with longer family duration on WIC. Duration of family WIC participation is associated with healthier beverage choices for infants and children, but does not appear to be equally beneficial across racial/ethnic groups in Los Angeles County.