Reading prosody is considered one of the essential markers of reading fluency, alongside accuracy and speed. The aim of our study was to investigate how development of reading prosody in Spanish children varies with sentence type and length. We compared primary school children from the third and fifth grades with an adult sample. Participants were recorded reading aloud a narrative text including short and long declarative, exclamatory and interrogative sentences. Recordings were analysed using Praat software to measure several prosodic features (i.e., pauses, duration, pitch and intensity). We found that third-grade children had not yet developed an adult-like prosody: they made more pauses, had a flatter melodic contour and had difficulty anticipating sentence structure. Fifth-graders displayed some features of adult prosody. Both length and type of sentence influenced the expressiveness of reading in the three groups. We conclude that reading expressiveness is closely related to reading experience and develops in a similar way to decoding and reading speed.