Mazel Tov!
Here’s another story of a kid somehow knowing that their mother was going to have twins. However, this story is told from the viewpoint of the person who came up with the prediction. The OP claimed that their family—the OP and their parents—would become a family of five.
And no, that didn’t include the new baby and the dog. Somehow, the OP knew that their mom was going to give birth to twin siblings. Probably thinking this was the imagination of a child, nobody took the OP seriously, but they probably stared in awe when their baseless prediction actually came true.