The Littlest Horse Thieves (1976)

When the owner of a Yorkshire coal-mine decides to mechanize to increase profits, the mine's pit ponies are scheduled to be destroyed. So, three children plan to steal them to keep them safe. But when they're caught, it's up to the mine owners and the miners themselves to decide what's right.

Unfortunately the movie The Littlest Horse Thieves is not yet available on HBO Max.