imo maybe it's because siwoo himself thinks that the vibe of his appearance gives a "scary, gloomy" impression to children (can be seen from the scene where the children run away when siwoo comes lmao), so the children who are afraid might complain to their parents and end up calling the police ╥﹏╥
For once Jaekyung could have denied him on humanitarian grounds (● ̄(エ) ̄●)