I have made myself 2 Ridgeview tees and my 6.5yo daughter wanted one too. So I took her measurements and shrunk down the pattern to fit her. She didn’t want the side slits so I knit it in the round up to the armholes and then worked back and forth for each section to the shoulders. I left the shoulder stitches live while I knit the front and then did a three needle bind off for the shoulder seams. Then I picked up stitches around the arm opening. I decreased every 10 rows 9x to give me about 13” for the sleeve.