Lost in Space "got campy" in its first season. It wasn't coldly serious for the whole year, and you can see the switch pretty clearly from fairly solid, straight SF adventure to wacky fantasy. The real transition from serious to comedy was The Space Croppers, when the Robinson's are visited by aliens dressed as hillbillies in a space ship that looked like a log cabin. From that episode forward, things got dicey. Suddenly Smith's comedy antics really took center stage. The main difference in season 2 was that the series became Children's Theater, with wacky monsters and colorful eccentric aliens.
Wow, there was a LiS episode called The Space Croppers? That was also used as the title of a Galactica 1980 episode. The writers of the latter must have been telegraphing "This series has officially become a lame, silly kids' show."