The Internet has become an integral part of everyday life, but analytical and systematic investigation of school-aged children’s online activities is lacking. This study aims to describe children’s Internet use according to types of online activities and examine the personal and family sociodemographic correlates of types of online activities within different sociocultural contexts. Cross-sectional survey data were collected from 840 children aged 8–10 years and their parents in Latvia, Lithuania and Taiwan. Children reported the frequency of using the Internet for ten specific activities, which were classified into the three distinct types of online activities, namely, information seeking, social interactions and entertainment, through multigroup confirmatory factor analysis. Overall, school-aged children used the Internet most frequently for entertainment and least frequently for social interactions, and Latvian children engaged the most frequently in all types of online activities. The multiple linear regression results show that in all three countries, children’s device ownership and use of the Internet to cope with negative emotions were the two most salient correlates of engagement in different online activities. Although family socioeconomic (e.g., parent’s education, financial status) differences in Internet usage types were not evident, there were country variations in the association of online activity types with family demographic factors (e.g., living arrangement, child’s number of siblings). This study identifies personal and family sociodemographic correlates of the types of activities children perform online and highlights differences in the comparison countries.