The process is described above, but it’s very hard to “innocently” end up with one of those images that they are looking for from the database.

And the way it’s being done (hashes), a collision is highly unlikely. If it does occur it doesn’t mean it’s similar in nature (e.g. innocent picture of own child in bath). The hash isn’t looking at the image content in the sense of “what’s in the picture”, just the bits of the file. So it’s highly, highly unlikely, even if a collision occurs, that the collision would be an image that happens to be another child innocently bathing.