Very interesting discussion indeed!
I don't think the kids necessarily try to change their accent, but that subconsciously, they know that to say things the Kiwi way will get them further. It's more a thing of, "do things as the Romans do". So they will adopt the accent because that's the way people here speak so they just do it too.
Now, you must understand, Jan & I left SA in '98 and headed to Texas. We had our kids there. Joshua, our eldest spent his first two years at home alone with me, and so had more of a South African accent in his speech. Later after having spent some time at day care and then school, he would be chatting to his friends and say in our "class" with the American "a" like in "cat". Then he'd turn to me, and automatically change to say "clahss" like the South African way "ah". So to him, without even consciously thinking of accents as such, he simply knew that "mommy speaks differently" and would speak to me as though I wouldn't understand if he spoke American!

With Heidi who arrived in our lives two years after Joshua, there never was a SA accent. She picked up on the Texan/American accent right away, as though she didn't have SA parents! It was kind of weird to hear her speak American!
As for Jan, there were some words that he had to change very quickly or he'd not make it in the working field... so "process" became "prahcess" very quickly, and "data" was "daytuh" not "Dahtah".

Myself - my American friends just LOVED my SA accent and would not listen to a thing I was actually saying, just to my accent!

I did eventually find myself changing certain things, like pronouncing my 'r's in words like "where" = "wherr" and saying pekaahn instead of peecun for pecan.
The city we lived in was Austin. To a South African, that is "awestin", but in American, it's "aahstin". So yeah, there were a few changes I had to make, but it took a few years! And I learned to say "y'all"

Now, we've been in NZ for a whopping 2.5 years, and Heidi was the first to start saying "wheah is my brush?" within 3 weeks of arrival! Joshua has a mixed accent - but he quickly learned to add the "-as" onto just about anything - cool-as, sweet-as, nice-as, super-as

And it's "Mom, can we go to the paahk?"
I haven't found anybody here not being able to understand me though, perhaps because when I speak English, I speak with an English-South African accent, and not with an Afrikaans accent. But they still pick up immediately that I'm South African.
On the other hand, when in the USA, all they knew was that I wasn't American... I'd get the following: "So, you'rre not from around heerre, arr ya?" or "So, wherr y'all from?"
and when you tell them, you get answers like, "oh, I have a cousin that's a missionarry in Rio"

or "That's in Africa, right?"

I once was told, "you speak English very well", and one of my friends was asked what it felt like to wear clothes!
So at least New Zealanders know something about South Africa, and recognize where you're from! On the other hand... sniff.... I've lost my "celebrity status" here!
