The study was planned to determine identifiable starting points of a trend towards obesity and the influence of variables in preschool children aged 0 to 6 years. In this longitudinal follow-up study, 102 children were enrolled. Anthropometric measurements such as weight-height centiles (specific for gender and age group), weight-height growth velocities, and body mass indices were taken annually and compared within each group from birth to 6 years. Family history and lifestyle variables were also recorded and compared. Our study has shown that gender does not affect the trend towards obesity. In obese children, the earliest sign of a trend was the rapid increase of weight and weight gain velocity after 6 months. There were upward trends in the BMI values indicating obesity at 1 year of age in boys and at 6 months of age in girls. The height was higher in obese children than in non-obese ones after 4 years of age. Paternal obesity and having an obese sibling were significant risk factors for obesity. In conclusion, 6 months are considered to be the most critical periods for evaluating the development of obesity in childhood. The efforts for preventing obesity should be initiated at 6 months of age.