I got this idea from 'The Preschooler's Busy Book' by Trish Kuffner. A fantastic recourse full of imaginative ideas for any parent/carer of young children. I refer to it almost daily.
Looking through old magazines, Finn and I chose a variety of facial features from faces (eyes, noses, mouths, eyebrows etc) and Finn arranged them on the page the way he decided. Then with a pen drew a face around the glued features. Your child could also add facial hair, ears, or any thing else to finish their creation.
Materials: Cartridge paper, glue, pens, magazines with faces.