One surefire way to keep a child’s attention during a song is to constantly change the tempo of that song. Whether I am gradually speeding/slowing down or doing so abruptly, even the most easily distracted students will perk up and listen.
Songs that abruptly change tempo are unpredicatable, and that element of surprise is what attracts my students’ ears. Often I will make up such songs on the spot as the children are playing a rhythm instrument; not only do they have to listen carefully, but they also need to adjust the tempo at which they are playing to match my singing and playing.
But my favorites are tunes made up of a single chorus that is sung gradually faster each time it is repeated. The words and melody should both be simple so that the song can be easily memorized. I’ve written several songs like this, but the most recent (and relevant to the season!) is called "The Leaves on the Trees".
My students love, love, love this "speeding up" song, and no matter how fast I play, they always yell, "Faster!". I give them shakers to play along, though any handheld rhythmic instrument would work nicely.