The "sensors" are just metal posts that go through the tank. You'd likely damage the walls of the tank itself long before you'd damage the sensors, and neither one is a concern with a sprayer hooked up to a garden hose. (If you used something like a pressure washer, that might start to be more concerning...maybe.)
If your kid is flushing wipes, the sensors and their readings are the least of your worries. I'd make sure that the tank did, in fact, get emptied, particularly if you don't have a transparent/translucent elbow to monitor progress with when dumping.
Spray wands are not expensive to buy pre-built, for what it's worth. You can get a basic PVC one for under $10 at Wal-Mart.