Ninja Kids (1986)

Lady Lotus, an evil sorceress, attempts to retrieve an ancient katana possessing great power from Naguchi, a martial arts master. Meanwhile, a group of friends are planning a camping trip to follow an all-girl class who are in turn on their own camping trip with their strict teacher. After several mishaps the friends are left stranded in the mountains. While navigating their way back, they stumble across a hidden cavern, where an old ninja master lives. The boys are selected to become ninjas and retrieve the katana that Lady Lotus is searching for.

Unfortunately the movie Ninja Kids is not yet available on HBO Max.