Deffinately the "cannon-ball possition" works. as has been mentioned almost every time. It is a great analogy too and is shorter than saying "ankles to your butt and hug your knees with your arms..." (i'm deffinately adding it to my teaching methods
Connecting your arms to your knees (most wrap arms arround) is a really nice thing because it helps your arms to stabilize your knees and it in turn helps your legs to stabilize your arms. also it helps you from going into a plow position.
a wakeworlder made this and thought it was kool so i'll post it.
One thing i will ADD (that i don't think has been mentioned) is figure out what foot is going in front.
if the kid has board background from other board sports than this will be easy as just asking them. if they have no boarding background than you can give them a little shove from behind and see what foot they use to catch themselves with, this will most likely be the front foot. most likely they will just naturally prefer one over the other when getting up anyway.
also when it comes to edging, i made this little illustration, but i look back on it and it has way too many words in it that can get confusing, but i think it has some good ideas in it anyway, and maybe someone else can bring something to the board that is easier and more visual like the "canon ball thing" that we can all benefit from as learners and teachers.
Now i like to tell people to play tug of war with the boat. no one has a hard time leaning on their heels and pulling away ( = HEEL SIDE EDGE) but lots have a hard time going toe side, or even straight for that matter. To go toe side, turn your chest away from the boat as if you are still playing tug of war with the boat, but instead of pulling backwards and digging with your heels, pull forwards as if trying to lean forward to walk/ pull it (the boat) in the other direction ( = TOE SIDE EDGE). --- It helps to show a visual with your own body while in the boat with a handle tied off short to something or someone--- This kind of explanation is usually only necessary for those with no boarding background. because telling people to "just lean on your toes to go in the direction of your toes and lean on your heals ...." just plain doesn't work