Worked size 10 years for a boy that just turned 7, made the sleeves slightly shorter, otherwise followed the pattern's measurements. My boy is not a tiny 7-year old, but he's not huge either, so looks like the sizes are a bit on the small side.
I think the sleeves are a little bit tight under the arms. The pattern says you can pick up some stitches under the arm and knit them together on next round, to avoid a hole (or you can sew after finishing). Next time I would pick up some stitches and work a few rounds before decreasing these sts.
Worked garter stitch brim in stead of folded brim for sleeves and body. I think it looks nice for this sweater,
and I avoided any purling and seaming.
Buttons from stash, too!