Words are seldom read in isolation. Predicting or anticipating upcoming words in a text, based on the context in which they are read, is an important aspect of efficient language processing. In sentence reading, words with congruent preceding context have been shown to be processed faster than words read in neutral or incongruous contexts. The onset of contextual facilitation effects is found very early in the first-pass-reading eye-movement and electroencephalogram (EEG) measures of skilled adult readers. However, the effect of contextual facilitation on children's eye movements during reading remains largely unexplored. To fill this gap, we tracked children's and adults' eye movements while reading stories with embedded words that were either strongly or weakly related to a clear narrative theme. Our central finding is that children showed late contextual facilitation effects during text reading as opposed to both early and late facilitation effects found in skilled adult readers. Contextual constraint had a similar effect on children's and adults' initiation of regressive saccades, whereas children invested more time in rereading relative to adults after encountering weakly contextually constrained words. Quantile regression analyses revealed that contextual facilitation effects had an early onset in adults' first-pass reading, whereas they only had a late onset in children's gaze durations.