How to tell the difference between crocodiles and alligators

Such things are important when you have young children, so I authored a rhyme (with help of a friend on Facebook):

Crocs always show both rows of teeth
And swim in salty sea.
When gators smile, you see a "U,"
With crocs, you see a "V"

With dotted snout in muddy swamp,
the Gator lies happily.
Crocs, with spots from head to toe,
Live life... estuarily.