Hard riddles for kids can be found through an online search, including this simple one: What starts with "P," ends with "E" and has thousands of letters in it? The answer: A post office.
Here's a difficult riddle involving logic: A man hangs his hat and closes his eyes. Then he walks 500 yards, turns around with his eyes still shut and shoots a hole in his hat. How did he do it? The answer: His hat was hanging on the barrel of his gun. Kids who love logic, math and sweets enjoy this one: A little boy has 210 candy canes. If the boy buys 10 more candy canes, he will have 220. He gave away 12. How many candy canes does the boy have now? The answer is 198, because the riddle said "if" he buys more. Kids who giggle at animals and nonsense get a kick out of this one: a cat and a mouse, a horse and a hippo, a giraffe and a gerbil are all under an umbrella. Which one gets wet? Answer: None of them, because it's not raining. Try this one at bedtime: What's that last thing you take off before going to bed? Answer: Your feet off the floor.