Hi Almohada --
When my niece turned 6 years old, I bought her a tacky touristy thing that she absolutely loves!
I bought her one of those "your name here" flamenco dancer posters. She loves looking at the pretty dancers and is impressed with seeing her name printed on the poster. My brother had it framed and she has it hanging proudly in her bedroom.
There is a tiny souvenir shop that will do it for you in 5 minutes right on Gran Vía on the same block at Casa del Libro. If you are facing Casa del Libro, it will be to your right on the same block at the corner.