It appears that your sentence is incomplete, but I can still provide some context and information based on what you've shared.

The statement "Surprisingly, no one knows how many children receive [something]" suggests that there's an uncertainty about the number of children involved in a particular situation or receiving a specific service or benefit. This lack of precise data could be due to various reasons such as inadequate record-keeping, varying definitions of "children" across different regions or organizations, or the difficulty in tracking certain populations.

If you could provide more details or complete the sentence, I would be able to give a more accurate and relevant response. For example, if you were referring to children receiving a particular type of medical treatment, educational service, or social welfare, I could elaborate on why this might be the case and what efforts are being made to improve the accuracy of such statistics.