I think the song with fewer animals is best to start off with. Remember to keep it simple. You can always change the song later or add on more animals if your class can handle it.
I was thinking about this and remembered some great resources I found a while back on the BBC site. Have a look at this link for Old MacDonald
. It's part of their Brit Lit programme. It's really great, there are flashcards, board games, songs, downloads and all sorts of things. A lot of it is too advanced for your kiddies with regards to their age but some of the resources should be useful.
Have a look around the site because there is also Red Riding Hood and Jack and the Beanstalk, if I remember correctly.
Let me know how it works out!