The Magician Trilogy by Jenny Nimmo

Also known as The Snow Spider Trilogy

I like Jenny Nimmo's writing and over all, this is a good trilogy.
It begins in the first book, the Snow Spider, with Gwyn's grandmother telling him on his 9th birthday, that he is a magician.  It contains Welsh folklore and Welsh words - which may be difficult for some children to read.
The 3 books get progressively darker and cover a time period of about 4 years following Gwyn, and his family and neighbors and relatives Emlyn and Nia. 
While I did like the stories, I found a few things about them disturbing and creepy. 
I did not like the fact that Gwyn's sister left to go to some other cold planet that steals children who are not happy and that when she returned briefly she did not want to stay with her family, but preferred to go back to her cold planet even though her mother kept her bedroom the same and her parents had never really gotten over her dissappearance. 
And I found Nia's obsession with her uncle and his dalliance with her older sister creepy.