The information requested falls within the responsibility of the National Statistician, who has been asked to reply.
Letter from Karen Dunnell, dated 20 October 2006:
As National Statistician, I have been asked to reply to your question concerning how many children are presently aged under five years. (95564)
The latest available data for the UK are the mid-2005 population estimates. The total number of children in the UK aged 0 to 4 years in mid-2005 was 3,427,500.