New Sand, For Now

We bought this turtle sandbox for the kids a couple years ago (used, off Craigslist, like 80% of the kids stuff we buy), and it's been growing in popularity.  Last summer Joshua was a huge fan, and Clara and Hannah kind of liked it at times.  This year, all three love it.  I recently brought it up from the basement and filled it with some sand I had leftover from last year.  I have a rule that they cannot remove any sand from the sandbox.  I'd hate to see how quickly we'd lose sand without that rule, because as it is, it gets depleted pretty quickly.  I think most of it is just lost due to careles sifting and shoveling, and that's okay, but I'm trying to eradicate things like filling a watering can with sand and then pouring it elsewhere in the yard.  The first batch of sand was pretty much gone as of yesterday.  That sand was good because it was the wetter kind that is more conducive to building sand castles and whatnot.  Today I filled the turtle up with new sand, but this is the drier kind that is not clumpy but is really easy to sift and pour, which I think they enjoy more.  Here they are enjoying their new sand, which I look forward to replenishing in a few weeks. :(