The Dark is Rising Sequence by Susan Cooper
The series certainly has won some very prestigious awards - two nominations for Newberry awards and winner of the 1976 Newberry for 'the most distinguished American children's book published in the previous year'. The five books in the series were published between 1965 and 1977, so I was just in their 'young adult' demographic (age 10 when the first one was published, still in college when the climax book came out).
Fantasy books were light on the shelves in those years. There was Tolkein and CS Lewis, of course, and tons of science fiction. But the genre that is now called 'urban fantasy' - where 'everyday people' are confronted with the mystic, the esoteric, or the fantastic - was not very common.
The five books are:
Over Sea, Under Stone
The Dark is Rising
The Grey King
Silver on the Tree
They chronicle the adventures of five children, three siblings, and two boys that they are introduced to by their 'Uncle Merry', Merriman Lyon, a mysterious figure with many secrets in his past.
The basic structure of the books is a series of quests - a Grail quest, a quest for the power over the elements, a quest for a sword, etc. There are many Authurian and pagan elements in the series that I didn't understand when I read them as a teenager.
This series re-read was a little disappointing. Don't get me wrong, it's a great children's series, but I kept wanting MORE - more detail, more history, more insight. Every now and then I run across a children's book that makes me want to read the 'grown up version'. These fall into that category.