A tiny couplet about the cheer Christmas brings, simple enough for the youngest listener to join in with. Two lines, one big feeling.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
Christmas comes but once a year,
And when it comes it brings good cheer.
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition