Is it my place to say something?

I would think there would be no problem with you saying something to the mother about the things the 25 yr old is exposing to the 9 yr old, but it kind of depends on the type of relationship you have with the family. Although she may have been watching an educational program, that is still inappropriate for a child to see. As far as the music, that too is inappropriate for a child to listen to. Even though it is just music, the words to matter because children listen and repeat these words, which in this type of music is usually very inappropriate. My nieces, which range from ages 1-11, have heard radio versions of these songs and can repeat many of the words, usually the words which no one would like their child to say. Even the radio versions of these songs are quite inappropriate for children, in my opinion. I would hope the mother of these children would not feel that it is okay for children to be exposed to this, or for her 25 yr old to expose her 9 yr old to these types of things. Good question and I hope you talk to this mother so she can tell her 25 yr old how inappropriate their behavior is.