I once had a NERF gun explode when I over-pumped the air bladder in it. I'm not sure if newer models would explode like that but for safety I would advise not trying to dis-assemble them while aired up. I have managed to take apart the good old NERF Maverick but they have redesigned that model a few times so my experience no longer applies.
@Montoya with not too much modification you could use a sandblasting cabinet as a real nice diaper changing station. You'd just need to run a pipe from the shoot at the bottom to a drain, put an exhaust fan in there on one side and a duct to vent the stank air out and away, cut a hole and mount a sealing diaper pail in there, and lastly you could run a pipe in there with a kitchen sink sprayer nozzle for extra cleaning power and to hose down the inside of station when you're done. You'd be protected from all the smells and rogue pee streams and wouldn't get your hands dirty.
Another way to dress up a Nerf, airsoft or other prop gun is to place a light stick or baton inside. Especially if there is an open slide, where looking in would reveal a nice glow in your favorite color (YELLOW on BLACK!) you can give an otherwise ordinary prop that look of a blaster. I have never used a baton, but these are electric and actually blink and create fluid motion.