Do you believe in magic? Caroline, Charles and Charlotte do, and nothing that happens during their summer holiday at their great uncle's house does anything to diminish that belief. There the Three C.'s find a wonderful garden and some very old books, resulting in escapades which do not necessarily please the grown-ups. E. Nesbit, as usual, transports us back to the hazy summer days of a well-to-do Edwardian childhood, liberally spiced with magic, humour and lessons learned. As Gore Vidal once wrote: ''...though a reading of E. Nesbit is hardly going to change the pattern of a nation, there is some evidence that the child who reads her will never be quite the same again, and that is probably a good thing.'' Published more than 100 years ago, this is one of Nesbit's least-known children's books, out of print for many years but now it is finally back