The Rs' back-line had been a major positive of late, conceding just two goals in five matches to aid their battle against relegation from the Premier League.
But they were easily picked apart by a rampant Swansea side, for whom Michu scored twice either side of goals from Angel Rangel and Pablo Hernandez.
"We made mistakes today. They were blatant, almost schoolboy errors to give the goals away," said Redknapp, whose side remain bottom of the table and six points from safety.
"Swansea are a good side and I love the way they play but I felt they didn't have to work hard for their goals. For the first goal we let Michu run inside and have a shot and when it comes back he has all the time in the world to scoop it back in.
"We get back to 2-1 and I'm thinking we'll get something out of this game and then suddenly we go and give another couple of poor goals away that should never have been conceded.
"Defensively we've been strong lately but today we weren't and it made it difficult."
Redknapp was pleased by the contribution of striker Bobby Zamora, who scored QPR's goal, but he admitted he was worried about relying on the former Fulham man, who has only just returned after three months out with a hip injury.
"He is what a Premier League player should be," added Redknapp. "He holds the ball, doesn't give it away and brings players into play. When he doesn't play we haven't got a focal point to our play.
"Jay Bothroyd has come back from loan and he is the only other one who could do that so maybe he needs to be given a chance."