Why is this the answer?

The answer is breath because this clever riddle uses fun clues to describe something you do all day long without even thinking about it. Your breath is the air that moves in and out of your body, and it is a super important part of staying alive. Let's look at the first part of the riddle: "Hard to catch, easy to hold." If you try to catch your breath, it is like trying to catch the air all around you. You can try to grab it with your hands, but air is too light and slips right through your fingers. It is hard to physically catch. But it is "easy to hold" because you can take a deep breath and keep that air inside your lungs for a little while. When you are playing a game like hide and seek, you might try to hold your breath to be extra quiet. This part of the riddle is a play on the two different ways we use the word "hold." You can't grab it like a ball, but you can easily hold it inside your body. Now for the second part: "Can't be seen, unless it's cold." Most of the time, when you breathe in and out, the air is totally invisible, like all the air in the room. You know it is there because you can feel the air, and you need it to live, but you cannot see it like a toy or a book. However, the riddle gives you one very special exception. Think about what happens when you walk outside on a very cold winter morning. When you talk or you blow out, what do you see floating out of your mouth? A little cloud of white mist! That white cloud is your warm breath hitting the super cold air outside. The cold air makes the tiny bit of water that is naturally in your breath turn into that small, visible cloud. It is like a secret trick of the weather that lets you finally see your own breath. This is why this simple, everyday thing is the perfect solution to this cool word puzzle.