Measuring sleeve length help?

I am making my second sweater. The first one was a top down and I did great, no problems. I measured the sleeve lenght under the arm and of course tried it on along the way for proper fit. Now I am making a child’s sweater. It is a cardigan. The sleeves are made by picking up the armhole stitches and knitting the sleeve in the round. I am decreasing every fifth row and all is well but I am not sure from where I should be measuring the sleeve length. Is it under the arm or from the shoulder? I am to knit eight inches then do the cuff.

Measure from under the arm. If it’s too long the cuffs can be turned up and the child will grow into it.

Thanks so much

When you pick up the stitches around the armhole and knit the sleeve down in the round wouldn’t it measure the same from any point from where you picked up the stitches to where you are?