TV Show about kid detectives

A young boy (12 or 13 maybe) moves to a small town in America after the death of his father. The show starts with him in the back-seat of the car and he's looking at the stars while his mum is inside a hospital getting keys to their new house. She is a nurse and i think they live in nurse housing maybe. He sees a comet sail through the sky. Next day he starts at school and is put into a group project with a boy and girl. I feel like the little girl is adopted and was wearing a red dress. The other boys name is Timmy and he is the sheriff's son. He has lots of siblings. The boy asks the two kids if they saw the comet because he thinks it crashed to earth nearby. They say no but that they want to investigate. I think there's conspiracy theory of aliens and the government is trying to cover stuff up. The kids end up forming a detective agency/private investigator thing and solve mysteries like missing cats etc. Set in the 50s or 60s maybe. Could even have been the 70s. The theme song is stuck in my head but only one line and I'm not even sure it's right. Something like "I loved you when you said goodbye"  or "I told you when you said goodbye" or something.