Grover does not drop the F bomb on Sesame Street or anywhere else.
What I believe Grover was saying is that's an excellent idea and not that's an F excellent idea although it sounds like it.
You just need to replay it and listen more closely because although at first it sounds like it I don't believe Grover actually said the F word on Sesame Street.
Even if he did it's not that big of a deal because kids will learn about those words anyway as they get older because remember we all were kids at one time and we are now adults and know all about those curse words.