When it comes to sand, it's easy.  Get "Play Sand".  It's just washed beach or river sand, a little coarser but without the rough, sharp edges found in mason's sand (little more than crushed silica, and silica=glass).  I'd wash it out in a bucket or large pan until it rinses clear, and let it soak with some ammonia in it for a day or so to just be sure.  Then dry it and toss it in.