As someone who travels regularly on a UK airline that for legal reasons has to seat kids next to at least one parent, I have watched the trend lately where many parents--who know what the policy is--rock up at the last minute to board, don't check in online in a timely fashion in order to assure suitable seats are assigned for them.
They also know they do not have to pay for their seat allocations to assure this by paying the seat reservation fee by the airline. Because those who did will be bumped for them on a last come first served basis.
These particular families have sussed the system and know that pax who have paid to reserve a particular seat or checked in online to cadge a seat (or are status pax who can choose a seat pre-24 hrs) will be moved at the last minute to accommodate the family-together requirement.
In these cases they exploit the last-arrived, first served situation where the airline is in a bind to seat a child and parent together for legal reasons.
The airline I travel mostly with has not instituted a fix for this problem of savvy parents exploiting the system either.
I am not anti-family by any means. But to put a stop to this nonsense, I think families traveling together need to be asked to step up to the plate and take on the responsibility to do what is necessary from the airline's point--in advance--to be seated together. The airline could set out a list of steps they need to take to get seats--like waiving the pre-24 hour restriction that single pax have for seat assignment and allowing them to get a group together at any time. That's more already than the non-status pax individual traveller has as a benefit.
Ergo, if a family rocks up at check in with no seats, they take what is on offer--or they are off loaded and sent on a later flight when they can be accommodated. Nobody gets moved for them because they thought their status as a family superceded everybody else's rights.
If it is a full flight and alot of gold card and silver card holders have selected seats--or non status folks have paid to reserve a seat--and these cannot be moved to accommodate kids next to parent, then the family gets off loaded.
You'd be surprised how fast this nonsense with families exploiting the system will get sorted. And believe me many are exploiting this system; I hear the crowing the comments on board.
I run into it all the time on UK-US runs. Families that regularly travel know the airine has to bend over backwards and abuse other pax's rights to the seat they paid extra for or status pax had coming to them.
A policy of offloads would sort this and this nonense would stop.
"Sorry Mr and Mrs X. You did not reserve seats as we asked you to, nor did you follow the pre-travel instructions for families traveling with children, therefore you will not be traveling with us today. Bye Bye."