help to identify fruit tree

Can anyone assist in identifying these fruit trees we have growing along the boundary fence of our new house. Large lime green veined leaves and round smooth fruit. see images of tree and fruit attached. I would like to know what is is and how best to care for it as these would make a great privacy screen with a bit more growth on them.
Thank you
Mermaid 16
Gold Coast Australia

 

Hmm, looks like Paw Paw (Papaya) to me

"The papaya (from Carib via Spanish), papaw or pawpaw is the fruit of the plant Carica papaya,..."
http://en.wikipedia.org/wiki/Carica_papaya

 

Thanks for giving it some thought Larry but we know that is not it. Fruit shape & colour is different to those. Anymore ideas?

 

I don't know... The tree says "Guava" or maybe "Sapote" but the fruit reminds me more of passifloras. Hmmmmm. Do you think it's a native or an import?

 

Thanks. Think you may be on to something with the sapote although inside the fruit looks different but it may be a version of that. Will investigate further.