Among the Sleep - Enhanced Edition

This is a lot less painful than it sounds. As there are only 2 instruments in the entire game.

House: Piano: As soon as you're thrown out of your cot, make your way out the bedroom, and use the stool to climb on to open the door. Then go through the door that's ajar, unplug the washing machine, and get Teddy. Make your way downstairs, and follow the hallway into the front room. Immediately on your left hand side, is a stool in front of a Piano. Climb up, lift the lid and press RB to interact.

Playground: Xylophone: In this level, once you activate the strange door in the playhouse, you need to slide down the pipe. Once at the bottom, you will have a Xylophone at your feet. You really can't miss it unless you're like me and not paying attention. Press RB to interact and a very easy 100g is yours for the taking.

Should this guide need revising, let me know in the comments below.

To unlock this achievement, you will need to interact with the Piano (Level 1) and Xylophone (Level 2).

The Piano is located in the living room of House (Level 1). After you save Teddy, you will go downstairs. As soon as you enter the first room, look to the left and climb up the small Piano stool. Open up the Piano and interact.

As soon as you open up the strange door in the playhouse, enter the pipe. You will load into Playground (Level 2). As soon as you land, the Xylophone will be on the right on the floor. Interact with it to unlock the achievement.
Note: You can select Playground (Level 2) from the chapter select and you will be place right next to the Xylophone.