My DBF has previously attended an evening AB book-signing event, to get AB's signature on one of the presents DBF gave me for Christmas. I have just asked him if there were folks with kids present for the signing (yes, but he doesn't remember how many, there were at least a few), and then asked if AB or the event organizers had those with children brought to front of line - and that was not done at least at that event.
DBF suggested (as I think did a PP) that this AB rule may have been the result of "learnings" from prior book-signing tours, which could be the case as AB has developed a pretty fair degree of experience in these events over the past many years (ten or so at least).
I understand and agree with the concept of not "rewarding" less than desirable behavior, and respect the opinions of those who would not agree with the following, which is my personal opinion: When I've gone to book-signings (not many, but a few and not personally been to one by AB), unless it's a children's book, for an evening event, I'd be fine with those with children going first as they are generally a small percentage and I'd rather not have a child melt down impact anyone; for a day-time event, I'd think all present should be addressed in order (adults without children present during a day time event are likely to have time constraints due to work requirements); and for a book-signing of a tome aimed at children, I would also think it most reasonable to have all served in order.
Of course, those are just my thoughts on what would be reasonable, and anyone organizing a book-signing or agreeing to perform one can make the rules they want, and those who want a book signed can agree or not to whatever the rules may be (limit on number, order of line whatever) in order to get a book signed.
I'd be interested in any updates from those who may attend a future AB signing, i.e. if the "those with kids go first) rule is applied. While AB has not announced (that I've seen) a signing in my area, I live in same area as AB, and as his next book is soon to be released, and DBF is well aware I'd love to have another signed AB book, I'll be glad to post update on any signing DBF may attend (it's hardly spoiling a surprise Christmas gift to let me know he made the extra effort to get it signed... as I've just explained to him, he just gets early extra points).