Whistle 1- On Level 1-3 when you get to the end of the course you will find a white block. Hold down while on top of the white block until you go behind the scenery. From here run to the end of the course and you will be transported to a room with a magic whistle

Whistle 2- On the World 1 Fortess, when you come across the first Dry-Bones, there will be a [] block. Hit this to get a leaf. As Racoon Mario, knock out the dry bones and fly up the ledge until you start walking along the top of it. Continue going right whilst on top of the ledge until you stop moving. Press up to be transported to a room with a Whistle

Whistle 3- On World 2 after you have collected the Hammer from the Hammer Brothers go to the top right corner of the world map. Use the Hammer to break a rock leading to a secret passge. In here there is a Firs Brothers, beat them to get the Whistle