At the very start of the game, when you gain control of Ethan, you will take Rose up to your bedroom and place her in her crib. After that, you can notice a yellow ball on the ground. Use your feet to kick this ball into the study which is the room connected to the bedroom with the computer on the desk. Make sure it doesn't get stuck on the doorway, or else you'll need to restart. The achievement unlocks when the ball gets to the other room.