Most sweaters in Harry Potter universe are hand knitted mostly using magic.
“We danced to this when we were eighteen!” said Mrs. Weasley, wiping her eyes on her knitting. “Do you remember, Arthur?”
“Mphf?” said Mr. Weasley, whose head had been nodding over the satsuma he was peeling. “Oh yes … marvelous tune . . .”
Harry Potter and the Half-Blood Prince, Chapter 16, A VeryFrosty Christmas
Hermione made socks for elfs, using magic.
“They're hats for house-elves,' she said briskly, now stuffing her books back into her bag. 'I did them over the summer. I'm a really slow knitter without magic but now I'm back at school I should be able to make lots more.”
Harry Potter and the Order of the Phoenix, Chapter 13, Detention with Dolores
Explicitly using magic.
“Harry glanced over at her; she was sitting with Crookshanks on her lap and chatting merrily to Ginny as a pair of knitting needles flashed in midair in front of her, now knitting a pair of shapeless elf socks.”
Harry Potter and the Order of the Phoenix, Chapter 14, Percy and Padfoot
Video evidence from the movie.