A Willow Igloo is a fun, easy, quick and free thing to do this winter. You must harvest the willow in winter when it is dormant. Go down to a river or lake edge and harvest some living willow branches. They need to be at least 2cm thick. Cut long lengths. Decide where you are going to build your willow igloo. A good place is somewhere which receives summer sun but does not dry out too much.
Use a hose or string to outline your design on the ground and then simply press the branches into the soil at least 10cm deep. Keep branches close together so that when they grow they will form a thick interwoven wall. A roof can be formed by bending over the tops of the willow and securing with string.
Keep igloo well watered over winter and in spring your kids will have a living hut to play in. I grow snow peas, sweet peas or runner beans up the outside in summer for my kids to snack on.
As the willow grows and branches, weave side branches through the uprights to form a thick wall. You could cut or form a window as the willow grows.