Toot Toot

he's 3 feet tall as of Twelve Months. That's around the same height as Maggie, when he started out as maybe 18 inches tall.

is Harry growing his own personally loyal Sidhe?

There's no way Mab hasn't taken notice of one of the weakest and most ancillary members of her court getting a huge power and respect buff from being personal guard to the Winter Knight.