Source: http://lifehacker.com/cut-a-watermelon-into-sticks-perfect-for-kids-and-part-1603562078
Summer's beloved fruit, the watermelon, can get pretty messy to eat. Instead of serving the melon in traditional wedges, cut it into sticks—easy finger foods.
This is great for little kids or for serving a crowd and you need smaller portions. I did this the other day and found another benefit: The sticks stack up much better in a container, so you don't have to do that Tetris-like watermelon wedges cramming to save space.
A Thrifty Mom has a tutorial for cutting the watermelon. Basically you'll first cut it into three pieces, then the intersecting 1-2" slices. If you have an apple corer
Watermelon Slices - Perfect for Little Hands | A Thrify Mom