The 26-year-old mother shared pictures on Instagram of her son getting creative on her beautiful face.
She was seen laughing and smiling in a collage of black-and-white photographs with lip gloss all over her chin and cheeks, reported E! online.
"Luca the make-up artist," she said.
Duff is known for posting pics of her son on social media.
Last week, she posted an adorable snap of the boy on the playground.