A small delicates washing bag is great when washing all of those tiny socks. This will keep them from getting lost in the towels and other clothes.
Pipe cleaners (the inexpensive kind from the craft stores) work great for cleaning the pipes and crevices of straws and drinking cups.
Magic erasers work best for cleaning crayon marks. Especially for cleaning crayons off the walls.
Baby powder helps sand come off super easy. Very helpful after a day at the beach when their bathing suits have a pound of sand inside and they are covered from head to toe.
Getting spit-up stains out of clothes can be a pain (and they reappear!). Mix Oxiclean and boiling water in a sink, then let the clothes soak until the water is cold.