The scary wary song made my 3 year old cry and she is not easily intimidated. She became very upset. I don't consider "fart" to be a bad word but I don't want my daughter going around singing it in a song either. She loves the site and I would let her listen to the other songs. I think parents should check the lyrics before allowing their children to listen. (You can do this on the site.)
An absolutely stunning site -- my daughter has been using this site (mostly Boowa and Koala) since she was not quite 4 -- highly educational and engaging -- she has learnt a lot. Highly recommended.