Time Slip Christmas!

Osborne, Mary Pope. A Ghost Tale for Christmas Time.
14 September 2012, Random House

Jack and Annie get sent to Victorian London to help Charles Dickens, in the same way that they helped Mozart, Louis Armstrong, and Lady August Gregory (who collected Irish legends). Unless they help, he won't write his most enduring work, A Christmas Carol. Disguising themselves as well-to-do boys, they try to get an audience with Dickens, but are sent away. They trade clothes with chimney sweeps and get into Dickens house. They follow him out into the town and are accused of a crime because they are grimy urchins-- Dickens shares with them how unfair he thinks society is, and how he struggled to make money gluing labels on pots of ink when his parents couldn't take care of him. Jack and Annie manage to convince him that his writing can change society, so he shouldn't give up.
Strengths: My own children adored these when they were just learning to read. The series started in 1992, so the books were fairly new when they were reading them. There must be 50 books now, along with the nonfiction companions for many, which are nice, short history lessons.
Weaknesses: Ah, history going wrong. A good excuse to time travel, surely, but really? These are all a little predictable, but that's why young readers love them.

Have a Merry Christmas if you are celebrating!