A 7yo can barely keep up with subtitles in their mother tongue, depending on the speed. And that's probably true for a p90 reader. A p50 there is no way it can follow subs understanding what they say. Now, being a video, they might be able to interpolate from what they see, so it might be a nice challenge. But doing this with subtitles in a foreign language is only for a few, privileged minds.

Source: father of a 8yo with VERY good reading skills (already reading books in 2 languages targeted at tweens)