Drawing and coloring for kids

My son loved playing the pets but really wanted the dinosaur pages but when I try tapping the purchase it won’t let me buy any of the locked pages- it lets me do the math problem then freezes on the purchase page

I like the way it is like you get all of the stuff but when and how do you get other level’s

When coloring the colored area does not match the place that I just tapped. When I tap the screen, the app puts lines of colors all over the screen. The app used to work perfectly and my sister spent many hours playing it. I think the latest update may have ruined the coloring function.