I respectfully disagree, based on anecdotes. The Dutch-speaking part of Belgium subtitles everything, except for shows meant for kids <8 years old. The French-speaking part on the other hand dubs everything, even interviews in the news. Guess which part of country sucks at speaking English.
My point is you need to watch the target language audio with no subtitle in your language.
If the choice is English-audio + Dutch-subtitle vs French-audio only, then of course there is no advantage to the second group. Try restricting the French-speaking kids to watch shows with English audio only.
