Is there not some shenanigans about having to obtain some form of paperwork when escorting a child who's not one's own?
I have sympathy with the OP: sometimes what seems, on the face of it, to be a great idea, leads to a great deal of undesirable and unforeseen logistics hassle.
Not to mention that I can imagine that having a 12yo in tow is going to have a dramatic effect on the dynamics of the getaway!