Ultra-processed foods (UPF) consumption has increased in recent decades, contributing to poor diet quality and certain health problems in early childhood. This study aimed to evaluate UPF consumption in 4-year-old children and determine maternal and child sociodemographic and lifestyle predictors of UPF consumption. We analysed data for 1736 mother-child pairs from the INfancia y Medio Ambiente birth cohort study. Children's diets were parent-reported using validated food frequency questionnaires from which UPF consumption was calculated according to the NOVA classification. We used multinomial logistic regression to assess associations between sociodemographic and lifestyle characteristics and child UPF consumption in tertiles (low, intermediate, high). The mean (SD) daily UPF consumption was 414.6 (240.2)g/day, accounting for 32.8 % of the total daily intake. The main sources of UPF consumption were ultra-processed dairy products (44.3 %), ultra-processed beverages (17.8 %) and sweet foods (16.5 %). A higher maternal UPF consumption during pregnancy [RRRmedium = 1.68 (95 %CI 1.23–2.30) and RRRhigh = 2.86 (95 %CI: 2.02–4.04)] and child television viewing [RRR>1.5 h/day = 1.65 (95 %CI: 1.21–2.25)] were positively associated with a higher child UPF consumption, whereas maternal age≥30 years was associated with reduced UPF consumption [RRR = 0.71 (95 %CI: 0.54–0.94)]. These associations remained similar when stratified by sex, although maternal age effect was not significant in sex-specific models. Medium and high UPF consumption of mothers during pregnancy, younger age at pregnancy, and more television viewing in children were associated with higher UPF consumption at age 4. The identification of factors associated with child UPF consumption could support the development of health promotion strategies aimed at reducing UPF consumption in children.