The last several flights I have been on, it has gotten sticky regarding our seat assignments. I have three children, 5, 14 & 14. Obviously I would prefer to sit with all three of them, but for whatever reason, Delta has had all four of us sitting apart. I usually have to reiterate several times, that my youngest absolutely cannot sit by herself. We were usually the last to be seated in the airplane, then magically they find several seats together. It can be quite nerve wracking. We had originaly had confirmed seats, but that flight was cancelled, so we had to make three layovers to get us to our destination and on all three flights, had to go thru the same thing. On all three flights, my 14 year old son sat far apart from us, and it made me crazy checking on him often. I felt sorry for the passengers around him, as he just loves to chat.
I don't know what the rules say, but I know in our case, it didn't matter. We were supposed to be "VERY" grateful, they found seats together for us. I just can't imagine a five year old sitting by herself. Geez.
On a side note, my husband, who flew on another airline, the same trip, had problems with his seats also. He way flying business class and both coming and going, they had two people with the same seat assignment, and of course he boarded after the other person, both times, and this caused quite a bit of confusion, and embarrassment on his part until they figured it out. He was supposed to get an aisle seat, and both trips ended up having to sit in a middle seat.
Seating arrangements can create quite a mess if handled improperly. Hopefully with our next trip, things will go much smoother.