Won't start - no power to accessories

Our 1999 Montana has a problem - it won't start, can't be jumped. When the key is turned there are no lights, no audible noise from the motor compartment.

Initial diagnosis is that the battery is dead. However, our friend's three year old was seen in the van, with a set of keys that were NOT the Montana's.

Is it possible that she tried the non-Montana keys and fubared the security system in some fashion? If so, what's the magic sequence to reset the thing?

Is this still a problem? If the security went into "lockout" you will have to wait an hour before it will let you start up again, or so i've heard....