Choose three or four keywords from each phrase of the song and write them on one side of separate word strips. Now choose a synonym for each keyword and write the synonym, in a different color, on the other side of the word strip.
When you are ready to teach, post one synonym from each phrase on the board. Tell the children that you will sing a song about these things but NOT these words. Challenge them to listen for the correct words. As they give the answers, turn the keywords over, singing that phrase again. Repeat, using the other word strips. Invite the children to sing with you as they are able.
You really don’t even need to divide the song into phrases, especially if it is a short song. Just choose several key words and write synonyms for them. Post them a few at a time so that you have a chance to sing the song several times.
This activity obviously works best with children who can read and who understand about substituting words, but if you use clear synonyms (not always easy) and explain the word, the little kids can also participate. I've used it in my combined primary and the kids like it. It works because the big kids don't always get it right away and I can remind all the children, including the younger ones, that "we are listening for a word that means the same thing as (blank)" So even those who cannot read can still listen.
This is also a great activity to use with a song that the children know, but which needs some review.