No gauge given.

From the pattern description: “The rib in this vest means that it will stretch over many different sizes and shapes, while keeping warmth close to the skin on cold nights.
Please use a soft yarn to make this a comfortable garment for the child.”

Direct link to PDF
Archived link to PDF ~ https://web.archive.org/web/20170319035800/http://knit-a-square.com/sites/default/files/Knitted_Garment_Roberts_Ribbed_Slip-Over1.pdf