By collecting and analyzing diapers, we identified a >6-fold increase in carriage of extended-spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae for healthy preschool children in Sweden (p40%. We analyzed samples from 334 children and found 56 containing >1 ESBL producer. The prevalence in the study population increased from 2.6% in 2010 to 16.8% in 2016 (p40%. Furthermore, 58% of the ESBL producers were multidrug resistant, and transmission of ESBL-producing and non-ESBL-producing strains was observed at several of the preschools. Toddlers appear to be major carriers of ESBL producers in Sweden.