How to knit puff sleeve?

I haven’t seen it anywhere, but I would like to knit a puff sleeve style sweater for my toddler. Anybody knows how to do it? Knit a flat piece, gather them, and then sew will be bulky. I generally don’t like seams. Any techniques to do it without seaming?

Like a sweatshirt sleeve?
The one I just did decreased 9 stitches in one row from a row of 43 stitches. Then it went into a ribbing.

I switched to DPNs to do the ribbing in the round.

For a puff sleeve you don’t exactly gather the top necessarily, but you do knit more sts than you would normally. If you have a pattern you’d like to change, we could help you with that.