My guess is that both sister and brother snuck up late playing around with the weapon and an accident happened.
Then Mom and Dad Ramsey, fearing the charges of neglect and/or jail time covered the scene up
Can a stun gun kill a child? I don't think "voltage" is an issue. A van der graaf generator packs way more voltage than a stun gun, and I haven't ever heard of a kid hurt by one (well, it gives quite a zap and your hair stands on end, but thats it.) My understanding is that it is amperage, not voltage, that will kill you.
Has anyone else heard of a child killed or even seriously injured by a stun gun?