Well, compared to Mylo anyway.
Here is Mylo, a few days before turning 5 months, in his XS hoodie:
And here is Willow today in the same hoodie. She is roughly 5 1/2 months (6 months on 28th feb):
Then her paws came out of the sleeves, she promptly fell over and ended up with her front legs out of the neck hole. I actually expected the difference to be bigger.