We estimate the effects of high-speed internet in early childhood development exploiting cross-cohort and geographic differences in the introduction of fiber-optic-to-the-home. Using variation in lifetime cumulative exposure to fiber optic and combining survey and administrative data, we estimate effects on cognitive and non-cognitive outcomes measured by validated screening tests. We show that an increase in 10 percentage points in lifetime exposure to fiber optic decreases development scores between 6% and 17% of a standard deviation in communication, problem solving and social skills. An analysis of heterogeneous effects shows that the negative impact is larger for children with more educated parents.