A kid gets kidnapped by a dog and is, later, held by the neck. This could be a little intense to some people because his life is endangered.
David lost his mom. This could be very emotional for those who lost their mothers.
The devil dog form eyes can change color. This can be scary. He is by far the most frightening character and even the first scene with him (where he's disguised as a different dog) is menacing bc his true nature is clear.