My kids all have their own preferences for pop songs.
My oldest (7) loves Taylor Swift's "Never getting back together" even though he hadn't even heard it performed by Swift-just what he overheard his classmate singing.
My 4 year old loves The Beatles "Hello, Goodbye," which perfectly fits his quite contrary personality.
My 2 yr old loves Queen's "Another one bites the dust" and "Bicycle" and Whitney Houston's "I will always love you." I have a really sweet video of him singing along with it, about 2 beats behind Whitney, at the top of his sweet little lungs, while swaying to the music.
I love all of those songs that I mentioned, but especially The Beatles--pretty much anything off their Anthology makes me happy to sing with them.
I also like to sing Shaggy's "Angel" song to my baby, substituting his name for "Shorty."