[/How have you created the APK's you send to your son?]
I used Paul's online tool that you mentioned and it worked very well.
In spite of using it to produce 5 APKs I stupidly failed to notice the line, "The following must be filled out if you want an APK suitable for submitting to the Google Play or Amazon store". My only excuse is that I was only trying to make APKs to send to my son
Now I'll get my brain in gear and use the whole of the online tool.
If I have any problems I'll use Naphier's guide. He has helped me out before.