My wife and I have been married for more than 12 years. We can manage a few hours seated apart just fine.
Thats understandable - its a few hrs and you are both adults. My flts are generally 14 hrs in duration, so thats a long time for parent and child to be separated, IMHO!
I just did. When my wife and I get split up, I will ask, politely, if someone would switch -- I always offer to take the less desirable seat and I immediately and graciously accept "no" as an answer. I would never sit in someone else's seat, never argue, and always phrase the request as a request, i.e. "Would you possibly be willing . . . ?" Frankly, though, it's not that big a deal -- we'll just sit apart.
Agreed ^. I do not do any of these things either - it is simply bad manners. A polite request is at best, all I would do and then continue as you have described.
Then you shouldn't have accepted the op-up. Your special need is that you sit with her. You need to make that happen without imposing on other people.
I think you have misread my post - at no time did I IMPOSE anything on anyone on my flt 
. In FACT we didnt even ask to switch, we waited (standing up not even taking seats) to see what transpired. As it turned out the couple who had one seat next to my daughter and one seat next to me in the MIDDLE block 25D wanted to swap, and it was a mutual initiation of swapping. They were also on an op-up and had no more right to better seats than we did - it was all equal. Again read my post please, we actually got the lesser of the deal as far as the seats were concerned, but as I was VERY grateful to even be in C class, I happily sat down next to my child in the middle block, thanking them, as they were thanking me.
If you got an op up (and you're here on FT) then you should know that seat location is a very big deal. Even if you didn't know, how could you assume that strangers wouldn't have to move to accommodate you.
No offense, but I find your tone to be one of assumptions towards me. Firstly, please look at my profile, I joined FT just over one month ago. The flight experience that I was describing was over one YEAR ago - so no I was not on FT and I did not know that seat location was that big of a deal. I didnt assume anything - I was told by the checkin agent, that we would be accommodated on board. At that time, I was not aware that it would be an issue, she had advised that many people had got the op-up and people were seated everywhere and that there would be swapping going on and it was no problem. Therefore I went ahead with the op-up. Hope that clarifies it for you.
As you note, this time it worked out. What would you have done if the couple didn't want to switch?
Why would they NOT want to switch??? They were NOT seated together either! One of them was seated next to me in 25D and the other was seated next to my daughter in 25G (bearing in mind that these rows are not adjacent to each other, but set back from each other and therefore not a clear line of sight).
You could have declined the op up. Which is more important -- sitting next to your daughter or sitting in C?
Clearly if I had been given the correct information at Check in and there was a remote chance of us not being able to fix this, I would have denied it. I didnt know any better back then. We are not all expert FTers like you.
I really want to know -- what would have happened if you couldn't find someone willing to switch? Would you have started explaining how your daughter can't remain calm if you don't sit next to her? Would you have said something like, "So, if you want to deal with her when she gets upset, feel free . . ."?
I would have spoken to the FA to find out what she/he recommended for us to do. I would not start throwing my weight around on board. That is not my style. I am polite and respectful.
How old is your child? If she's too young to tend to herself, yes I would. I wouldn't start there, of course -- I would tell you and the FA exactly what I planned to do first. It's not my goal to make trouble for you. I will not switch, however, to a lesser seat to accommodate you in a circumstance like this.
Why do you think it's appropriate to impose on someone else, forcing them to switch to a seat that, for them, is undesirable, so that you could accept an op up? That is the very meaning of entitlement demanding.
Answered you above. Please dont make assumptions about me and what I was supposedly doing. You do NOT know.
I'm sure things are different in Oz. In the U.S. you'd be in for a most unpleasant time.