When I was young, my mom always cut up the watermelon in triangles with the rind attached. Yes it was easy, but also created a big mess for little hands to eat.
I always get asked how it is done so the other day I took pictures!
FYI - if you have a flexible cutting board....that is the one to use. It is much easier to get it into a bowl without a mess if you can bend your cutting board. I got a set of two from IKEA for super cheap!
Once your watermelon is ready...cut it in half.