it need an idiom that means the oposite of

[Unregistered]

an apple doesn't fall far from the tree

[Anglika]

Not easy to find one. This is the best I've come up with so far:

Travel broadens the mind

[mykwyner]

The metaphor about the apple not falling far from the tree alludes to children being similar to their parents. I can't think of an idiom or other type of saying that alludes to children being different from their parents.

[Tdol]

I suppose you could say that someone is 'not a chip off the old block'.