Game crashes all the time within 5 minutes of opening a world.

Whenever I open up MineCraft to the main page it's completely fine. The main page and settings are working perfectly for me. But unfortunately whenever I open up a world I've created or am continuing the world ends up crashing about 5 minutes into playing. Sometimes it will lag a bit and then go to a black screen for about 5 seconds then crash, but other times it will just crash out of nowhere. This happens every single time I play MineCraft PE. It's been happening for mostly my iPad mini but sometimes it will also happen with my iPhone4S as well. I've only got one world on my game and I've already tried to delete then re-download MineCraft itself but unfortunately nothing has changed. Please fix problem soon 😞( Thanks.