Food and beverage marketing drives poor diet quality and obesity risk among children. However, it is unknown how much young children are exposed to digital food and beverage marketing on mobile devices like tablets and smartphones. The objective of this study was to estimate how frequently young children, who are particularly vulnerable to advertising, view food and beverage marketing while using mobile devices. Seventy-five 2–11-y olds and their parents from Massachusetts participated in this cross-sectional study from 2022 to 2023. Average estimated exposure to food and beverage advertisements and food/beverage brand appearances was calculated for 5 consecutive days using a combination of battery screenshots and average estimates of marketing collected from children’s devices. Generalized estimating equations tested for sociodemographic differences in advertising exposure. Young children’s estimated exposure to food and beverage advertisements and brand appearances on mobile devices was highly variable, with many children seeing none on a given day but a substantial minority viewing large amounts. Estimated exposure depended on how much a child used either YouTube or a gaming app; there was no exposure on other apps used by children. Higher parental educational attainment was associated with substantially reduced risk of a child viewing 2 or more food or beverage advertisements or brand appearances on a given day (adjusted odds ratio = 0.26, 95% confidence interval: 0.10, 0.70). Certain children, particularly those from households with lower parental educational attainment, may be at risk for high exposure to digital food and beverage marketing, whereas other children may have minimal risk. Future research should explore exposure in more diverse samples with valid, feasible measures.