Rounds are fun “group” songs, where different people (or groups of people) sing the same song, but starting at different times. Traditionally, the “leader” will begin singing the song. As the leader finishes the first line of the song and begins the second, the next singer (or group) will start singing (at the beginning). Each time the leader begins a new line, another singer (or group) starts singing at the beginning of the song, until four different lines are being sung at the same time. The last person (or group) to start will end up being the last one(s) to finish, singing the last line all by themselves.
I remember singing rounds for (what seemed like) hours at a time as my mother and sisters and I traveled “over the river and through the woods” to my grandparents’ house. That and the Alphabet Game combined to make the two-plus hour trip pass much more enjoyably.