I think you asked this on AL too? One of the admins has posted this on the Q&A:
The number of children shown for Adoption Link on our statistics page is purely the children that social workers have chosen to put on Adoption Link. When we relaunch this site in 2 or 3 weeks time there will be also be a summary of national statistics on that page, and I have pasted the text from this below:
In England, 5,050 children were adopted from care during the year ending 31st March 2014, compared to 4,010 in 2013. (Source: BAAF) At 30th September 2014, 3,470 children had a placement order but were not yet placed (a 26% decrease from 31st March 2014). At that time is was estimated that there were more adopters than children children waiting. (Source: Adoption Leadership Board quarterly data) At the beginning of March 2015 there were 630 children on the Adoption Register for England. (Source: Guardian Social Care Network) 27 children were matched by the Register last month. (Source: Adoption Register for England, March 2015)
In Wales, 345 children were adopted from care during the year ending 31st March 2014, compared to 329 in 2013 - a 5% increase. (Source: BAAF)
In Scotland, 297 children who ceased to be looked after in the year ending July 2013 were adopted. (Source: BAAF)
In Northern Ireland, 89 looked after children were adopted in the year ending 31st March 2014 (up from 88 in 2012-13 and 60 in 2011-12). (Source: BAAF)