How do we eliminate bugs in my 2-year-old's sandbox?
This is a tough one. You need to replace the sand with some sand that has been sanitized. Put all of the old sand in the garbage. Before adding the new sand, spray the box with an insecticide, and keep your daughter away from the empty container for 48 hours. Wipe the lip of the box that will be exposed after the sand fill with a detergent. Rinse well, as this part will be in direct contact with those little hands. The container should drain well so the sand stays as dry as possible.
If possible, move the sandbox to another part of the yard. The bugs could be sand fleas or they could be fleas from cats that came in despite your best efforts to keep them out. Rake the sand regularly with a sand rake to pull up hidden attractions such as an old cookie, cat feces, or a half-eaten lollipop.