As hoped I finished the hat in time for the trip to the mountain zoo. The skull and crossbones are vintage blanket wool felt appliqued onto the (shop bought, as my knitting is nowhere near this level!) stripey hat. I googled for jolly roger images and found one like this here at Hello Yarn (thankyou!!), so i drew a quick pencil sketch of it and then just cut it from the blanket freehand.
Cute enough for a little pirate I am sure you will agree.