In this film, both characters are around 12 or 13 years old. The girl’s behavior starts to change the more she hangs out with this boy. At some point they got these plastic (toy) guns and decided to rob a toy store they were in. They both took a pair of roller skates and other toys and then went home roller skating. At the end, I remember they plotted to rob a bank. On that same day, a real robbery was occurring at the bank these two kids were planning to rob and one or both of them got shot. I cannot remember.
I think I saw this movie in the late 90s or early 2000s. It was in color and I am pretty sure it had been filmed in Mexico City.