slimboyfat:
Here is just one example. For Chile in 2002 the Witnesses reported 60,701 publishers. Yet in the census that year 119,455 reported themselves as Jehovah's Witnesses. That is much more than simply counting children as well, indicating that the Witness figures are actually quite conservative. That is not an isolated example - the same pattern of more Witnesses self-reporting occurs whenever the census asks for specific denominational affiliation. By contrast the Mormons always find that far fewer report themselves as Mormons than are claimed as members by the church.
The average fertility rate in Chile is 2 children per female. If just half of the publishers in Chile have only one child (likely to be higher), that takes the total number of people reported as Witnesses up to 90,000. So it is not remarkable that children may indeed account for most, or nearly all of those reported as JW in the Chile census.