The Snow Spider Trilogy.
"Time to find out if you are a magician!" said Gwyn's grandmother... "Time to remember your ancestors: Math, Lord of Gwynedd, Gwydion and Gilfaethwy!" On his ninth birthday Gwyn is given a brooch and told to cast it into the wind. High on the mountainside, Gwyn hurls the brooch into the air and waits... It is only later that Gwyn discovers the wind has sent something back: the snow spider.