Apps for relaxation techniques: Chill Outz®, Smiling Mind, Headspace: Guided Meditation and Mindfulness , https://www.happify.com/ and https://www.calm.com/.
An app about coping with anxiety: MindShift
Calming sounds and yoga: Super Stretch Yoga HD, Enchanted Meditations for Kids 1 and Relax Melodies.
Please refer to this site for more information. https://www.eastersealstech.com/2017/04/19/chill-outz-relaxation-techniques-children/