SOLVED. YA book where polar ice caps are giant monsters [s]

[Kris]

Here's a long shot - Exodus by Julie Bertagna?

How old was the child (or children)?
Was it a realistic location? U.S. or elsewhere? On an island or by the sea?

[Sue]

Were the children shape-shifters? My first thought was the 'Switchers' trilogy by Kate Thomson.
"One of the best books of the year' said the Guardian when Switchers was published and it received outstanding critical acclaim, followed by great sales. Kate Thompson went on to write two more unputdownable sequels Midnight`s Choice and Wild Blood, featuring Tess and Kevin, and here are all three novels together in one volume for nine-year-olds and above. Tess and Kevin are Switchers - they can change into any creature at will. And when they discover they share this gift, they find that together they have powers beyond belief, enabling the two of them to save the world from icy destruction. But there are other more sinister characters among the Switchers and when Tess is dragged into the dark night-time world of Martin, she finds herself facing the most terrifying choice of her life. What is more she is approaching her fifteenth birthday, at which point she must make up her mind about who or what she will become in her final permanent Switch - from which there is no going back-"