Wow. This sounds crazy.
So glad I'm in Australia where most airlines have their auto-seating systems turned on and you are automatically seat assigned together (if on the same PNR).
Otherwise you can call up and put in a seating request and this will be manually done by the airport staff.
And finally of course there is online check-in so that you can check in yourself if you like.
If there were children seated in between strangers I would definitely be moving people (as cabin crew). Even if the flight is full it is not acceptable at all for small children to not be in the same row as their parents.