The NSPCC in the UK have some published estimates for the rates of child abuse in the UK. This covers all types of abuse, not just sexual. According to their website:
There are currently over 50,000 children identified as needing protection from abuse in the UK
Over 62,000 children and young people talked to ChildLine about abuse last year
We estimate that for every child identified as needing protection from abuse, another 8 are suffering abuse
This is in a population of around 64 million. If you are to assume that the congregation is pretty much a reflection of society in general then a very rough calculation of the UK membership (130k) and the worldwide membership (8mil) against the estimated figure above ((50000*8)/64000000) gives around 800 children in the UK and 50000 worldwide as needing protection from abuse now.
To be far to the other posts, this is not exactly comparing apples with apples. This is not purely sexual abuse and there is no real way of knowing so even this type of calculation is hardly scientific but even reducing the numbers by an highly optimistic 90% is chilling.
I think it's clear that the numbers will always be speculative but what the figures from Oz do show is that the problem is not limited to a short period of time and not insignificant. If there is any similar numbers worldwide then the scale of the problem over the decades is frightening.
There has to be a small band of brothers that know the real figures globally and I bet they are absolutely terrified that there is increased publicity on this and what that might mean in terms of legal exposure.