The trailer for the Happytime Murders is admittedly funny, but the idea of children’s television characters acting inappropriately has a long history in television and movies.
Here’s a scene from the ‘Smiletime‘ episode from Angel (1999).
And Who Framed Roger Rabbit (1988) revolved around cartoon characters interacting with the ‘real’ world–as opposed to puppets–though the same idea of subverting tropes typical to children’s television are still evident.
And there are certainly others. I’m sure that there are television shows and movies that I haven’t included here (you could even go back to the ‘Living Doll’ episode of The Twilight Zone (1963) and the Puppetmaster (1989) franchise.
Though, back to The Happytime Murders. As I have already stated it’s not nearly as subversive as it likes to think that it is though to be so all they had to do is include Muppets that people are already familiar with (like Kermit the Frog, Miss Piggy and so on) though there’s no way that Disney (the current owners of the Muppets) would allow them to do so.