Photo by the great Sharon Montrose (Lucky us!)
I think some fantastic toddler costumes can be made very simply using solid colored matching pants and shirts, with just one or two other accessories. That way, if the costume does become a favorite, it's easy to wash, easy to get on and off in a hurry, and comfortable for play time.
Here's a picture of Ruben from last year, when he needed a quick NEW costume right before a Halloween party (!):
(photo credit unknown)
This year our costumes will be a little more elaborate, but I do love the simplicity of these old favorites.