Reddit mentions of I Can Handle It (Mindful Mantras)

I Can Handle It by Laurie Wright

Listening to My Body: A guide to helping kids understand the connection between their sensations (what the heck are those?) and feelings so that they can get better at figuring out what they need. by Gabi Garcia

Breathe Like a Bear: 30 Mindful Moments for Kids to Feel Calm and Focused Anytime, Anywhere by Kira Willey

Edit to add a French book: Léon et les émotions by Annie Groovie!

Not programs but some little things I have found to help -

Cosmic Yoga (youtube channel) has some meditation routines for kids - https://www.youtube.com/watch?v=ZBnPlqQFPKs

also I had students in the past that were calmed down simply from watching jelly fish swim to calming music - like this https://www.youtube.com/watch?v=SmfbP17xyqQ

also found this book to be useful (depending on the age of your child) - https://www.amazon.ca/Can-Handle-Ms-Laurie-Wright/dp/099524720X/ref=sr_1_12?crid=1I7JP9BSMNB1O&keywords=anxiety+workbook+for+kids&qid=1563833004&s=books&sprefix=anxiety+workbook%2Cstripbooks%2C165&sr=1-12

Not exactly what you described, but possibly also appealing: I Can Handle It by Laurie Wright.

It's a whole series, though I've only read this one so far with my son. It's not exactly about working hard if that's specifically what you're looking for, but it is about feeling capable of handling what's going on around you, so it can be a confidence-builder.