I've seen it in communities I've visited. (And not just those into diaper fetishes.) Legitimate Mommy types with little boys.

It appears to be a different fetish though, with a different motivation... most Daddies deal with a Little Princess who is unwittingly naughty and in need of correction... little boys are, of course, just naturally naughty and dirty minded and need stiff discipline.

Both are different, imo, than "traditional" D/s in that these are sub-centric models.