The mother-of-one posted the first piece of footage alongside her growing young boy, and captioned it: "My dude."
And in the second boomerang, the Younger actress showed off her playful side and appeared to be tickling Luca.
"When Mum attacks," Duff captioned the cute footage.
Fans were quick to comment on the intimate moments she shared.
"Well this is a cute moment!" one wrote.
While another commented: "He looks like your twin when you were younger."
Duff, 30, shares Luca with her former husband Mike Comrie, 37. while the two divorced after six years of marriage, the two remain amicable as they co-parent their son.