Once upon a time, no one around here even knew what a “diaper” was. Now I hear people talking about changing diapers rather than nappies (I hope it doesn’t take over entirely. I hate the word diaper).
That’s another worrying one I hear too, although not from teenagers.
Yeah lexical replacement is a big worry, though what worries me more is the influence of American phonetics. I wonder if Aussie will be rhotic someday!
I blame wikipedia, they usually default to the American word.
For example, if I search for nappy
Aussie has always been more American than English was: there was a major trade route to the American west coast, and many Californian miners came over for the gold rush. It is still obviously different from an American accent: there is no Australian accent that I would confuse with any American accent.
But the modern Aussie accent, and the modern English accent, and the modern NZ accent are noticibly less “English” than the 1950’s accent. Compare any recordings of the Queen from 1950 and 2000.
Also, half the people I work with don’t have Aussie accents at all: according to the 2011 Census data, about one-quarter of the population was born overseas. Their children have an Australian accent, but it’s a different Australian accent.
And – people from NSW or Queensland think that the rest of Australia don’t have an Australian accent anyway.
I suspect that Australia was populated by Europeans too late and too homogenously to have much accent variety, certainly as compared to the variety that exists in the UK or US. The variations based on area are modest (Adelaidians tend to pronounce terminal Ls as Ws, for example). There are slight differences in word usage that are local (terms for beer glasses, for example, although that is becoming more uniform in recent times).
The real differences in accent are class and education based. Essentially there is broad Australian (think Bryan Browne) and educated Australian (think Malcolm Turnbull and Kevin Rudd - they start about 1.00 in).
Any changes therefore may well be more noticeable because of initial homogeneity to begin with.
Kids tend to follow the same pattern of accents, but the word content often follows American fashion, to some degree. In my house, you can hear the ankle biters say “totes awks” and “Whatevs” and “amazeballs”, but they do so with an Australian accent. That pattern follows, in my experience, with whatever basic version of the Australian accent they started with. I think they pick up expressions that sound amusing, and they are made even more amusing by being said transgressively in an Australian accent.
As to Australian turns of phrase, I have no doubt they are cycling out, but they have always done so. I can remember using the expression “fair dinkum” unironically in 1982 to a Canadian (who responded by saying “I didn’t think people actually said that!”). I can’t recall hearing any spontaneous uses of it in conversation for years. All the “stone the crows!” and “flat out like a lizard drinking” phrases are fading. Still, politicians tend to keep them on life support in order to sound like men of the people. Thus, “rort” and “furphy” will be with us for a long time.
And the well-spring is not dry. I am fond of “about as inconspicuous as Liberace at a wharfie’s picnic”, which obviously dates from no earlier than the 70s. Rugby Union’s Honey Badger (Nick Cummings) is keeping the spirit alive.
I, personally, am doing my best to keep the phrase “As flash as a rat with a gold tooth” alive. It’s my small contribution to the majestic English language.
Dang. Very impressive. Give that man a beer! 
Accent wise, no. The “American” accent we’re exposed to relentlessly in the TV and Movies is generally a sort of flat neutral accent.
Slang terms, yes and no. My kids were born early 90s and can use a lot of American terms interchangeably with Australian terms and usually know which is which. Mind you if I hear either of them referring to the space at the rear of their car as a “Trunk” rather than the Boot, I’ll slam their heads in it.’
Fries are generally the shoestring cut things that Maccas or Hungry Jacks serve, whereas normal sized chips are chips.
Subway do not make Sandwiches.
Yeah, a lot of the really old 40s and 50s slang terms and idioms are fading out (except for Alf Stewart in Home and Away) but I’m still fair dinkum about keeping some alive and kicking.
So summary, no, Aussie kids are not starting to develop American accents.
My dad said the same thing about me and I’m 48, also his dad was horrified that he would listen to that horrible American rock and roll.
Meh it’s been going on for years.
I overheard a youngish woman the other day telling her children she was looking for the ‘elevator’. Now, I have no problem with Americans calling it an elevator but why would an Australian person use a four syllable word when we have a perfectly acceptable one syllable word?