Just one problem with this theory of Miscavige's. He's supposed to be this enormous, powerful, luminous, high-toned being, right? And the thetans (spirits) in these children are supposed to be degraded ones who have taken birth in new bodies?
Then (according to his theory) why aren't they afraid of him?
The original plan for Halloween 2019 was to have David Miscavige ambushed by a gang of trick-or treaters. This would've caused detrimental effects to David's entire being, seeing as he believes that their Body Thetans (attached spirits) will swarm him! LOL
IMHO, migration of BTs is a very definite possibility, although I don't see why children should be more of a source of migrations than anyone else.
But DBs are chock full of BTs (that's a major reason how DBs get to be DBs in the first place) and they do want to migrate if they can. LRH didn't want DBs around him for that very reason.
The recently died is another source of migrations. In this case, they have to get out and find a new host because the old one just isn't hostable any more. What I would consider to be a severe punishment would be to set a cage in a graveyard and make someone stay in it overnight. Lots of BTs would jump on them and by the morning they would be a "miserable mess".
I believe the COS came up with "Solo NOTs at home" because they didn't want BTs parking themselves in the Sandcastle, where they would jump onto any unfortunate being that came along.
EDIT: I've always wondered -- does a woman who gives birth transfer some of her BTs to her baby?