... if I had kids I'd work twice as hard with the kids so they would understand the water/energy issues of our times ... and I'd argue, if your kid is going to stand under the showerhead masterbating for long periods of time, having an EFFICIENT showerhead would definitely be a better way to go ... 

The big hitter EASY change is the toilets.  Denver Water buys 'em for ya, sweat equity is FREE.  Plus, when I bought our house, the toilets were PINK.  Sinks, PINK.  Everything is non stomach churning WHITE now ... I loved dumping that old toilet that used 4 gallons a flush get picked up by a junk collector truck within 15 minutes of it being put there by myself.  Our new toilets use .4 gallons a flush.  EASY MONEY!!!  INSTANT ROI!!!