People share a lot of resouces in Internet, so you can find a song in a website and a didactical propose in another. This is a example
Didactic:
http://www.teachchildrenesl.com/songs.htm
Song:
http://learnenglishkids.britishcouncil.org/en/songs/old-macdonald-had-farm
In this website you can find a lot activities for this song
The song is very important for me to primary or english class because you can put in a song a lot of vocabulary or the vocabulary that you are preparing with your children.
The pedagogical use of the song makes learning fun for children. It´s a motivation idea to learn English