Watch the video below that reviews deep breathing:
Initially, focus only on having your child slow down their breathing by having your child do the following steps:
If your child feels dizzy, light-headed, or uncomfortable, STOP and breath normally.
After your child is able to slow down their breathing, they can start to focus on moving their belly with breathing:
With younger children you can have them hold their favorite stuffed animal on their belly and describe that you would like to take their friend for a ride. In order to have their friend go for a ride, they need to have their belly go up and down through their deep breathing. Have them fill their belly up by breathing in and watch their friend go up. Then slowly have them let their friend go down by breathing out.