Me too. For the flight from Narita to HK, 4 separated seats for my 2 children (4 yrs old and 6 yrs old), my spouse and I when online checkin. I informed Delta staff when airport check-in. The staff said that they will arrange adjacent seats but not guranteed all in the same row. The staff said the staff at the gate will arrange. Finally, we got 4 adjacent seats in the same row. My advice is to have earlier airport check in and arrive at the gate earlier.