Go to your room! I mean it. I'm very very cross with you. I'm very very angry with you! Time our! Go to your room! Go... to... your... ROOM! I'm really glad that worked. Those would have been terrible last words.
This is one of those wonderfully daft-yet-obvious moments that only Doctor Who can get away with, and that Steven Moffat at his best creates like nobody's business. Because of course a monster that is basically a scared child is going to be fended off by someone pretending to be an angry parent. Of course, the genius of the moment is that it's only an obvious thing to happen after the fact and after you've spent a little time thinking about it, which means it's both unexpected and a fitting resolution to the cliffhanger from The Empty Child. It also shows off the Doctor's resourcefulness and willingness to think outside the box, something present since the earliest incarnations of the character, suggesting that the soul of Classic Who is very much present in the Revival. That's not to discount Eccleston from this, though, as he makes what could be a diffcult speech work on screen. His serious delivery of the first part helps the audience to suspend their disbelief and buy into the moment and then his cheeky delivery of the last sentence diffuses the tension brilliantly.