This is a free UK pattern which is mainly done in half-treble stitch.

Any double knitting yarn can be used, providing the tension can be matched approximately.

Choose a soft yarn — toddlers soon discard scratchy hats!

The hat in the picture was made from 1 x 50 g each of red, white, and blue, which will probably be enough yarn for at least two hats. This pattern is ideal for using up left–over balls of yarn, so feel free to use whatever colours you feel go well together.