aclarkaz, I don't think you'll be happy with teva's in such a long stretch of water.
The spider sci-fi
tevas are best in my opinion. Even with those you still slip-in-slide inside the carraige. It's amazing how much tighter you need to adjust the velcro straps. Neoprene socks would do the trick! I never thought of that. They're about $18-25 at surf shops. Should be available on-line somewhere.
The only other concern is velcro doesn't hold well in water. You need an itty bitty rubberband to keep the velcro from seperating. Teva's used to always come with a set. I'm sure they're available for a buck or two if they still make 'em. If not, just pick up some tiny rubber automotive gaskets. Though those gaskets are resin'd for heat and chemical stability as opposed to elasticy.
If that's all too complicated...the easiest thing would be an old pair of running shoes. Forget the boot idea all together if they're leather or you'll end up a new set of toddler sized boots.