Khan Academy for kids app

I recently downloaded Khan Academy for Kids App because kindergarten course not run on the laptop but it needs android phone.  I downloaded Khan Academy App - APK file from the internet and installed on Android phone, first time application run fine. But after few minutes it crashes. I restarted my Android phone and Khan Academy App for Kids but when I select my child name, I see picture running, running, running.... but nothing after that, no error, no movement beyond that...please help me.