After 1900 he concentrated on painting, encouraged by Whistler. He was knighted in 1936. Ben Nicholson and Nancy Nicholson were his children; as was the architect Christopher 'Kit' Nicholson.
He was involved in illustrating early volumes from Robert Graves, with Nancy. He wrote and illustrated characteristic children's books: The Velveteen Rabbit (1922) by Margery Williams, and his own Clever Bill (1926) and The Pirate Twins (1929) for Faber & Faber.
External link:
Cover of Clever Bill at http://www.adh.brighton.ac.uk/schoolofdesign/MA.COURSE/01/LIANicholson.html