I’ve got this excellent idea for a decades-spanning prank to pull on future children. The idea is that you raise your children while giving little clues along the way that they were adopted. Eventually you admit to them that they are adopted while they are still quite young, and you raise them in a loving fashion “just like their birth parents would have”. As the years go past, they are happy but they always have this unfulfilled curiosity about their real parents.
Eventually they leave home and in their adult life they begin to research their birth parents. They get in contact with the adoption agency and the agency tells them that their birth parents are willing to meet with them.
They set up the meeting and when they arrive, you’re there waiting for them, and you fall to your knees and cry out:
“I CAN’T KEEP THE TRUTH FROM YOU ANY LONGER… YOU’RE NOT ADOPTED!”