While there is a very good chance his mother's habits damaged his brain, there are ways you can make things better.
Firstly, have him practice on focusing. Daily. Not like Jedi training or anything, but maybe get a course that can help him develop his focus and critical thinking abilities. The earlier you can get him started the better off he will be.
This will help is cognitive thinking and with enough practice he might be able to combat the problems obviously passed down to him by an irresponsible mother. It's not a quick fix by any means, but might be able to allow him to remember things for a longer period of time.