In the digital age, the internet has become an essential source of information gathering and maintains a network of social contact. In this paper, we use microdata from the China Family Panel Studies to examine the effects of guardian's internet use on teenager's cognitive skills. Using mobile internet users and base station density as instruments, we found that guardian's internet use had a significant impact on teenager's cognitive abilities as measured by math and verbal tests. Heterogeneity analysis shows that the impact is more substantial for guardians in rural areas and less-educated guardians. Further exploration of the mechanism shows that internet usage affects cognitive skills through monetary investment, time investment, and parental environment. The result suggests that promoting internet usage for less educated families in rural areas can potentially improve children's academic performance and decrease inequality across regions and generations.