In the present study, we investigate semantic knowledge of both adults and children for early learned words. Previous studies have suggested that semantic knowledge forms a network with particular properties, called a complex network. Since, in theory, a particular kind of network structure may be generated by a particular process, the structure of the semantic knowledge network found in semantic tasks has been supposed to reflect the developmental process of semantic knowledge acquisition. However, at this point, no empirical description is available for the development of childrens knowledge --adult substitutes are used. We investigate childrens semantic knowledge using an alternative-forced-choice association task. The result suggests that the childrens semantic network is closely approximated by a random network which is different from adults network. However, it is not truly random but contains a reliable structure. We discuss a possible developmental trajectory from a childrens random-like network to an adults complex network.