It's not a stretch to assume all 10 adults will prioritize the 8 children over the welfare of the rest of the plane. You should have split the reservation. I wouldn't have said anything if I was on the plane and it was obvious parents were in the exit row. An emergency is super unlikely for me to mention anything to the FA.
Let's say the plane is going down and your children or children's friends are crying for help and maybe dying too. Your primary duty is to open the damn door, get off the plane right afterwards, and not to go backwards delaying and blocking other passengers trying to avoid dying to rescue your child or your child's friends. Your three adults are definitely not able and willing to perform the duties required in the exit row if the children are dying elsewhere in the plane.
The GA had to do what she had to do. It's not giving every customer sunshine and rainbows. I'm guessing the other GAs didn't catch it or didn't care enough.
if my 14 year old is on the plane I don't sit in the exit row even if my wife is on the plane with my 14 year old and even if our PNR is split. A. it seems to violate the spirit of the regulation and B. my wife would kill me 😛