I enjoyed this episode a lot. And unlike other Doctor-lite episodes, this one was actually heavy on the Doctor, which in a way was disappointing, cause I would have liked to see a fully realized story with Jenny and Vastra as the leads. I saw part of a great idea in here with Jenny being the action heroin while Vastra is the brains, with Strax as the comic relief, if indeed they are eying this trio for a spin-off, I know I'd definitely watch it.
As for the inclusion of the kids (and their subsequent use in next weeks episode), I have no issue with it at all. I've always felt the tone of Doctor Who was one for all ages, and to include children in the cast (or at least one episode) makes sense.