Steven Moffat wanted to introduce a new kind of Weeping Angel. They were also called babies when Rory was sent to them. So it's possible they are baby Weeping Angels.
This is the first time we've ever seen Angels in an established, seemingly thriving community. Because it is the first time, we don't know much about what they're like in those circumstances. That, however, is certainly when they'd be most likely to have their young with them.