You might want to read the entire article you’re linking to, since it doesn’t seem to support the narrative you are trying to posit. Especially this line:
”The results of these checks don't give a picture of how accurate the given age of all asylum seekers in Sweden is, as the checks have only been carried out in cases where there was reason to doubt the person's given age.”
So your statement that “most of the 'child refugees' they were admitting were over 18” is, in fact, not what the article says. Instead, what it does say is in those cases where the Swedish authorities suspected the person’s age was not in fact under 18, it turns out their suspicions were correct.
The authorities were doing their job, in other words.
In fact, the story doesn’t actually even claim these people were intentionally lying. It states that one possible explanation is that, during the eighteen months between the time the applications were originally filed and when they were considered, those people had simply aged past eighteen.