Is it always children? I've been reading some of the J.S. Fletcher mysteries from here and he seems to frequently make his main characters do remarkably stupid things so the villains can capture them and explain the whole mystery.
I mean, if you knew that two people were brutally murdered nearby possibly regarding buried treasure, would you romp about the countryside investigating ruins? Unarmed?
And then the villains are even dumber, because they don't kill the idiots, but instead explain everything, only to be foiled at the end.
I guess that's common in a lot of fiction, but it's aggravating.