Echosmith is an American indie pop band composed of four siblings: Graham, Sydney, Noah, and Jamie Sierota. They are best known for their hit song "Cool Kids", which reached number 13 on the Billboard Hot 100 and was certified double platinum by the RIAA in 2014. The Muppets and Mike Tompkins performed an a cappella cover of Echosmith's "Cool Kids" in a YouTube video posted on May 4, 2015. (YouTube)