My understanding is that children rewatching things over and over is healthy for them, as it aids in things like language learning.
Anecdotally, in my own experience learning a second language, the online part of the course will play an audio or video clip, then play it again and have you answer questions on it, then do it again having you fill out missing words in a transcript, then play it again as you read the text along. I've found this extremely helpful to tune my ears.
