My theory on (most) reviews is that you only ever hear from the whingers. And lets face it, there seem to be a lot out there :)
Air travel outside of business/first class is always going to be challenging, especially with kids.
I have never had a major problem with Qantas, I no nothing of Virgin Atlantic. Virgin Blue, which flies a lot of cheap domestic routes in Australia is okay, but I would prefer Qantas any day (but would usually expect to pay a little more). You may find yourself on a Cathay flight anyway as they code share out of HK.
Personally, if I found myself in your shoes, I would probably not buy the extra seat (we are living on a very real tight budget) and then spend the whole flight kicking myself over it (and having my husband kick me for it too!). You might need to file the extra expense under "Life is too short not to....."
