Trying to get a figure of children with their biometric fingerprints on school databases is hard to estimate as the data on percentages varies according to statements from LEA's, manufacturers and Freedom of Information (FOI) requests.
But from this article Labour councillor Denise Headley uncovered 15 of Edmonton Green borough’s 92 schools using the "controversial biometric identification system".
In the same article Andy O'Brien, Managing Director of Micro Librarian Systems, states that 30% of schools use the fingerprint scanner. Is that Edmonton Green schools or just all schools? - because the figure from Edmonton Green is not 30%.
Working on 23%, which is just about in between the above figures and is also the percentage of schools using biometric databases in Suffolk from a recent FOI request, the following figures apply:
UK school population: Approx 9.5 million children.
23% of the total is 2,170,680 children.
So I think it it fair to say that over 2 million UK children have their biometric data on schools PC's. Maybe more.
I'd be very surprised if there are 2 million+ consenting parents to this.
http://new.wales.gov.uk/docrepos/40382/40382313/statistics/schools/1152752/key-edu-2006-e.pdf?lang=en link broken, see http://wales.gov.uk/docs/statistics/2011/110126sb72011en.pdf