Sleaves for baby cardigan

Please help me, knitting gurus! From where it says “increase on each edge” I’m so confused! I’m doing the green. What does this mean???

After the the initial increase of 4 sts across the row (call this row 1) increase at each edge on rows 11,21 and 31 then on rows 39, 47 and 55. That’ll be 12 sts increased and take you from 38 to 50sts.

Thank you so much! My head was about to pop off!