There was this wonderful book that I read when I was around 11 or 12 and it had some similarities to the Narnia series. I lost the book when my family moved and I can't remember the title of it. (this was about 12 years ago) I thought that maybe someone on this website may have read the book as it was written in a similar vein to the Narnia series.
What I remember from the book is that there were 2 or 3 children and they were in an attic room where there were old television sets. (I think it was set in London during one of the world wars as well) They turned on the TVs and each saw different scenes. One was of a medieval dungeon where a man was chained and another was a forest (I think). The one child touched the screen where the man was imprisoned and was sucked into the TV and ended up in the dungeon with the prisoner.
The prisoner turned out to be some sort of prince or noble and was guarded by a serpent that could shrink or grow at will. The child helped him escape and they went to look for the others.
If this sounds familiar to anyone please let me know, half remembering the book is driving me crazy and I'd love to read it again!
Thank you. :)