When you breathe in, your tummy fills up with air, just like a balloon. This air has oxygen, which is super important for your body. It travels through your lungs, which are like spongy air filters, and gets sent everywhere in your body.
Then, when you breathe out, the air pushes out the used-up oxygen and makes way for fresh air to come in.

Example

1. Take a deep breath and breathe in and out.
2. Take a deep breath, and smell the flowers.
3. Fish breathe underwater through their gills.