I'm fairly new to LOL (been playing for a few months), and I can confirm there is usually at least one bot on each team. You can usually tell b/c they don't have keystones. And no, they aren't new players. I'm assuming they are people running scripts to level smurf accounts up. It's pretty easy to spot based on how they act in game. Example: team fight going on and they just run right into the middle of the enemy team and die repeatedly.
I was actually in a game where I was the only "player" on the team, and several times it's been just me and one other "player". It's bad.