I'm using it for the substrate, because I was just using regular peat and nothing else, and there was no drainage, so it became stagnant.
It also started to smell awful! Oh and the reason for me being curioys why it could be harmful is it has silica in it.
ive used play sand in the past for aquariums but it does contain extremely small particles which if ingested could cause serious problems. not a great idea IMO. you can get a bag of turface at your local tractor supply for about $15. the particle size and fact that its not silica ensure your animals will remain healthy.
I wouldn't be concerned about the safety of play sand with the frogs, however it probably won't solve your drainage problem. A false bottom that doesn't allow water to wick up into your substrate but allows it to drain away is (in my opinion) the easiest way to prevent your stagnation problem.
I don't know of any specific risks of using sand in your substrate, however, I will say this. If you are going to use a commercially available product labeled "PLAY SAND" rinse the hell out of it. By that I mean, when you are done, rinse it several more times. Several years ago we were setting up an aquarium with some rare Tropheus. We used a commercial play sand. We rinsed it in the tank, but only enough that it ran clear. The fish all promptly died overnight after having been doing well in our quarantine system for several weeks. It turns out the sand had something added to it, I forget the name, that was a mold, bacterial, fungus inhibitor. This was to retard said organism's growth in a sandbox.
Personally I wouldn't do it. Search this site or google ABG (Atlanta Botanical Gardens) Soil mix. This stuff works great. As long as it is well drained, ie over a false bottom or hydroton, it shouldn't smell like anything other than good soil.
I've used sand in the past for a lizard tank. I believe we purchased it. Before using it I rinsed it repeatedly until after it rinsed clear. I then baked it. I had no problems with it. The tank wasn't super wet though and it wasn't submerged as it was in Doug's use for an aquarium.
Also, the only risk to using sand that I am aware of is impaction if they consume too much in a short period of time. Typically this is done while they eat their food they miss and get some sand in the mouth. It isn't always a problem but could happen. If it is mixed in with peat, especially in such a small quantity, the chance of that happening? much smaller. I'm not aware of other problems that James mentions.