Can you give me some information on buying a karaoke machine for my 9 year old grand daughter?

I’m on Amazon think some of the products I’m looking at are just the CD’s. Others appear to be just the microphones. I’m really confused…do you have to buy “special” CD’s, or will any CD work? Obviously I don’t know much about Karaoke. Any info you want to give me would be greatly appreciated.

PS Yes the girl can SING. She’s 9….