Has anyone ever done any research into the proportion of children who have these 'imaginary' friends? If that proportion was sufficiently high, could it not be a indicator that the research that the 'Children - religion the default position?' thread is about is more than just pie in the sky?
Actually I had considered bringing up the notion of children creating invisible friends in the 'Children - religion the default position?' as evidence to refute the notion.
So it is correct that without an overt steer from parents, other adults or society in general many children create an invisible friend during a stage in their development. And indeed this it probably the most common occurrence of that sort - other beliefs tend to be much more overtly linked to societal input and acceptance.
But it is massively stretching the point to suggest that this is evidence that the default is that children 'raised alone on a desert island would come to believe in God'.
The first and most obvious challenge is that an invisible friend is not god - far from it. God is supposedly a supernatural and powerful being, perhaps involved in creation etc. The invisible friend isn't that at all - it is typically just what it says - an invented friend - another child rather like the child themselves or their real friends. So belief in an invisible friend cannot be thought of as belief in god because an invisible friend is not god.
The second issue is likelihood. The invention of invisible friends isn't uncommon - I think stats suggest perhaps 40% of kids create one at some time. But this is no-where near enough to argue that it is the default position, which would require most or nearly all to have one.
And finally I am not convinced that the creation of an invisible friend is entirely linked to societal influence. As children are brought up they are exposed to all sorts of examples of people and things which aren't actually real (in a living sense) - whether through stories, or tuning cuddly toys into loved characters etc etc. So against this backdrop I don't think it is unexpected that the child themselves (who at that stage in development will not have a great grasp of the difference between real and imaginary - that comes later) creates their own character. Some might align it with a cuddly toy or doll, others may do it without the need for a 'prop'.
And finally from a anthropomorphic and developmental point of view the create of invisible friends and other types of 'pretend' character used in role play fits perfectly within the evolutionary driver for the development of advanced social skills as we are inherently a social species. No god required for an explanation.