Kiwi accent comes back to bite me

I am a born and bred kiwi, although I've been living in Australia for 10 years now. Eek, where has that time gone?? Anyway, one would think that would be enough time for kiwi my accent to be overtaken by my Aussie accent, and for the most part it has. It takes a keen ear for someone to pick, yet the odd person notices it immediately.

So, H, my 4 year old, has lived with me his whole life. Of course he has, I'm his mama right? So he should know how I speak, yes? Well this has happened twice now and it makes my husband fall on the floor laughing each time.....

Me "H, where's that little car that has the pen in it?"

H "What car, mama?"

Me "The one with the pen in it."

H "The pin?"

Me "No the car with the PEN in it, you know, your new one".

H "The PEEN?"

Me "No, the PEN. You know, the one Aunty A gave you?!"

H "The pin?"

Me "The PEN, for drawing, in the car Aunty A gave you!"

H "Oh, the PEN!"

Pen, pin, pun....sheesh!