"Making whoopee" is perhaps the dumbest euphemism ever for having sex. To me, it makes me think of whoopie cushions, which makes me think of farts, which, not to be a kinkshamer, but is not a very sexy thing in my mind. It sounds silly and ridiculous. It also sounds like something that no one would ever use in the real world...but lets look at some history.
I know the phrase, like probably everyone under the age of seventy, from The Newlywed Game, a racy game show where couples tried to answer questions about each other's personal lives---with the obvious questions about newly married people's favorite pastime, euphemized as "making whoopee". Said television show was one I watched in reruns during daytime television when I was home sick as a child, which is really the only reason why someone should be watching The Newlywed Game. I would have guessed that the expression was made expressly for that show, but in fact, there was a popular song, of the same name, dating from a play (simple called "Whoopee!" from 1928 that was made into a movie in 1930. In the song "Makin' Whoopee!" refers to the festivities of marriage. The song was covered as a jazz standard for the next thirty years. Perhaps, along the way "Making whoopee!" was a popular euphemism for intercourse, but the thing about slang from 60+ years ago was that it was not written down or publicized, so whether it was actually a popular phrase that people would have understood, or whether it was something that Chuck Barris and Bob Eubanks more or less created out of an old random phrase is something I don't know.
Two things I do know: first, the "naughtiness" of the 60s and 70s, which was probably daring and fresh at the time, seems tacky, smarmy and coy, and the wink wink silliness of the phrase "making whoopee" is emblematic of that. The second thing I know is about sex education: kids are going to learn about these things anyway, and it is really a matter of whether they are going to learn real information, or whether they are going to learn a series of euphemisms and veiled references from daytime television shows watched while home sick.