You're aware that your family is exploring a huge UNEXPLORED area? Sorry they don't spoon feed you how to find the secret areas. That doesn't make it bad design. It fits the bill.
Your clue in LotW's case is "some walls may not be walls. find them"
alot of games of the era are "guilty" of this, because the games came out at a time when spoon feeding the player wasn't around yet. No colored text for important parts, or hints to tell you where to go next. No scooby doo looking secret walls.
Back when the adventure games required alot of thought, and effort. People toughed em out just fine. Spoon feeding and helping the player along is a fairly recent thing, and I think its stupid to be honest.
I cant imagine playing a game like Ultima and having half as much fun if the game told me all kinds of clues without having to search em out.