I have only explored the German section of this site, but it has many other countries/languages. It incorporates contributions from visitors to the site so it keeps growing all the time. There are lyrics, sheet music and even audio files of chidren’s traditional songs and rhymes, so you don’t have to know the tune or even be able to read music to learn the songs. I’m trying to introduce my 2-year-old to German but am very far from fluent so learning some songs and nursery rhymes have worked well for me to find ways to incorporate the language into our day.
I hope some others find it helpful!