There are few people more near and dear to a busy, famous mother than her prized nanny. Finding someone who truly loves your kids, and understands their needs and limits with equal parts tenderness and discipline is harder than it sounds. So, once you've got a good one it makes sense to hold onto them tight.
That being said, it makes total sense for Jennifer Garner to feel protective of her good nanny relationship. Particularly, when the cuteness of Chrissy Teigen's kids functions as a potential threat.