IMO it all depends on the kids behavior.
I remember one flight where our family was headed to Hawaii. There was a family of 5 in coach with us as well. The parents were in the row ahead of the 3 kids. The younger one acted up the entire time and the other two provoked him. I can still hear them yelling "Henry!", and this flight was back in 2008. On our return flight home, there was another extended family on our flight that was also on the flight there. At the gate, the grandfather commented that he hoped Henry and his family were not on our flight again;)
I also remember a flight home from Paris and the kids were fine, but the mother, oh my! We were on the upper deck of the plane and there was a ledge along the wall of the windows. The mom behind me proceeded to put her bare feet on the ledge all the way up into my space. I should have spoken up, but you would have thought that me shoving her feet away, etc would be been a clue.
So it is't just kids that can be awful.
For us, we always stayed together as a family, and still do. Our kids are grown adults, but we still travel together on occasion and we either all go premium or economy, we don't split up. My husband is always getting upgraded due to status, but he won't leave me in the back.