Minecraft does not open

We have an IPad (A1458) and iOS 10.3.3. We update the Minecraft app October 30, 2019, version 1.13.  

When we start the Minecraft app we see the Mojang logo. Then the screen is white and after a while the app closes. 

My son loves to play Minecraft and is so worried that everything he has built is gone. 

We would be very grateful for help with our problem. 

Best regards 

Sara Werner