The Doctor Dances (2) - S1-E10
[The Doctor, Capt. Jack and Rose are cornered by the empty children.]
The Doctor: Go to your room. Go to your room! I mean it. I'm very, very angry with you. I'm very, very cross! Go to your room! [The children lurch away.] I'm really glad that worked. Those would have been terrible last words.
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.