Maybe the neighbour’s wife died in the car accident and the neighbour become depressed and started acting violently towards his children, so they ran away. Scared. The neighbour soon realised this and put missing posters everywhere. A demon (the weird black thing) said that it can bring his children back and so, the desperate neighbour agrees for the demon to help him but instead, the demon made the children scared and end up killing them. The boy was killed by the demon(?) and the girl died in a rollercoaster. The neighbour got mad at the demon and locked it in the basement so that no one will experience the same thing as he did So maybe the neighbour was only trying to protect you? Idk it’s just a theory (my English is not that good,sorry)