I have boys who are about the right age to start reading The Hardy Boys. The older son is reading the first one and claims “it’s a great book, lots of action.” So, for nostalgic reasons, and to talk to the 3rd grader about it I picked them up to read along with him.
First, the language the characters use between one another is dated, there can be no hiding that. That and the stories (mysteries) are somehow solved by the boys in giant leaps based on assumptions with almost no clues.
But remember, these weren’t written for adults. They were written for kids. They were great to get kids to think. My son is starting to try to figure out how to solve the mystery before the Hardy Boys. But, the best part is, he is excited to read.
Don’t worry about them being dated (unless you have the originals and then there is some racism taken out in the later versions). They are good books for kids, and they do nudge the kids to read more. Give it a shot! You have the recommendation of at least one 3rd grader.