I think this will be more of a software problem than hardware, which is what the systems forum more focus' on.
Is it necessary that the footage be recorded to a central location? Just I imagine it would be quite simple to to get three "nanny" cams and set them up. They would have a fairly long battery life and could record footage internally, then it would be fairly simple to retrieve it later on.
Otherwise I imagine something akin to a home security system would suffice. Most even have options to turn on/off at various times, upon sensing motion and such.