Zearalenone (ZEA) is a mycotoxin that acts primarily as an endocrine disruptor. Biomonitoring studies are needed to assess exposure and risk, particularly among vulnerable groups. This study reports two pilot biomonitoring surveys of ZEA in 38 lactating mothers and 42 children (5–12 years old). Both were associated with a questionnaire to collect data on the sociodemographics and eating habits of the participants. About 76% of urine samples were contaminated (188.12 ± 235.99 ng/mL), with the hazard quotient reaching 2.36 in the worst-case scenario for younger children. Of the analyzed breastmilk samples, 55.26% were contaminated (158.26 ± 77.50). A statistically significant association between ZEA contamination of breastmilk and the maternal consumption of wholemeal bread, cereal flakes, sausages, smoked meat and pork was found, suggesting that these foods are determinants of higher exposure. The hazard quotient in the worst-case scenario for breastfed babies under 16 weeks was estimated as 0.61. Results confirm frequent exposure to this endocrine disruptor among these two vulnerable groups in central Portugal, showing the need for further studies.