The Veldt

What is the purpose (point) of the story?

I'm wondering about whether it is to prevent the technology or just about the relationship between children and their parents.

The story does not suggest that we should prevent technology, but that we should not let it control us; we should not rely on technology to replace our human relationships such as between parents and their children.  In this story, the children's humanity is destroyed as their parents are destroyed by the technology in the room, they are cold and have no remorse or regret; they are as cold as the technology that controls the room.