I'm working on a large sandbox for my kid and the neighbours' kids to enjoy (it's a big Millennium Falcon). I've managed to design it so it's just wood, large 12" structural screws, and some large galvanized carriage bolt plus nut and washer couplings.
I chose to make the entire thing out of spruce 2x4 planks, since pressure treated pine wouldn't make sense, and I opted not to go with cedar since some kids might be allergic to cedar oil.
What is a good stain or resource for info on stains I could use on my masterpiece? My concern is small kids getting it on their hands and putting their hands in their mouths, so it has to be completely non toxic. For wooden utensils, I've used mineral oil and walnut oil, but for something going outdoors, I need something else, and I'm not too familiar with stains and protecting outdoor furniture.
Also, should I pre-treat each spruce board after cutting to length/shape, or can I just treat the finished product, and not have to worry about the unexposed areas?