In South-Eastern Asian countries, the remarkable decrease in fertility is one of significant demographic phenomenon of the last decades. Still, child labour is sees as a crucial, pressing issue that pervades the developing world. In this thesis I study the link between the demographic transition - fertility and mortality decline that took place in Thailand recently and the changing pattern of work for school-aged children. After a description of the situation and a review of the literature, I focus on an empirical analysis of panel data on the Nang Rong district. Results are in line with the prediction that fertility decline along with economic development has a positive influence on parental choices about the economic activity of their offspring.