Learning Latin can be fun - more and more schools realise how important it is for children to learn Latin.
It is the basis from all medical and scientific terms, as well as being the official language of the Catholic Church for 1600 years:)

You can learn simple hymns like the Ave Maria (The Hail Mary) using downloads from here at Gregorian Chant for Kids

here for example are the words (with how they sound shown underneath) and music for the:

there are 10 other hymns in Latin like this on the chant for kids website above

More on teaching gregorian chant to children via the Justine Ward Method:

this 24 minute lesson well worth a watch