Objectives: The gastrointestinal tract constitutes a complex and diverse ecosystem. Escherichia coli is one of the most frequently studied and characterised species in the gut ecosystem; nevertheless, there has been little research to determine their diversity and population dynamics in the intestines of children over time. We analysed the turnover or dominant E. coli isolates in children faecal matter during 1 year. Methods: In this prospective study, a fresh faecal sample was obtained from children longitudinally over one year (30 faecal samples at sampling period 1 and 22 faecal samples at sampling periods 2 and 3). From each stool sample, five E. coli colonies were randomly selected (n = 405 E. coli isolates total) in order to characterize the genotype and phenotypic antimicrobial resistance patterns. Results: We were unable to find same E. coli dominant clone in faecal matter from 30 children in different sampling periods. Whole-genome sequencing of three isolates belonging to ST131 found in one child during the sampling period I and II indicated that isolates were three different ST 131 clones that carried extended-spectrum β-lactamase (ESBL) genes. Conclusion: We found that all numerically dominant E. coli lineages in children's intestines were transient colonisers, and antimicrobial resistance phenotypes of these strains varied significantly over time without any apparent selective force.