Q:

How do you prompt the user to set the default home app

I have been searching the net for the past few days and so far I have not come up with much.  What I want to know is how do I get the box up where you can chose the default home app.  I currently have not seen how to get this dialogue box up on a button click(for instance). 
EDIT: The dialogue I am talking about is the one used in toddler lock, looks like this. 

A:

Your app have to serve as regular launcher.  If there will be more apps of that type (which usually will happen as you'd be 2nd one), Android will ask you by itself on first return to launcher.  There's no way to show that dialog from your code. 
EDIT
I do not know "toddler", but to get this effect it shall suffice to act like launcher (by settings CATEGORY_HOME) and then, when user launches your app for first time, you instantly redirects him back to launcher.  At that moment Android finds out it got more than one launcher and pops up that dialog.