Here's a reply for those wondering. They're working on it
Hi,
The problem you are describing is because of iOS 10. We are aware of the problem and I have implemented a fix for it, however, when we tried to release the fix to App Store, we realised Apple has put a requirement of a 64-bit version for any new app released to App Store. I have started to work on it, but it requires me to go through most of the code, and any third party solutions we use, so it has taken more time than we first though. Sorry!
Unfortunately I cannot give you an exact date for the new version, yet.
Algodoo is free on PC and Mac (unless you buy it from the Mac App Store), so if you have a computer, your son can play with Algodoo on it, for free:
http://www.algodoo.com/download/