I am in a similar position in that I am researching an ancestor who, following Trafalgar, was captured aboard Le Formidable and who was subsequently paroled at Tiverton. My current task is to find evidence confirming he is the father of two boys, born in Tiverton, during his stay, one of whom bears his first name and a corruption of his surname; but I digress.

Having had the opportunity to visit the National Archives at Kew, I found the experience somewhat daunting but the staff helpful.

The following document may help to clarify the archives a little: "A guide to the naval records in the national archives of the UK", Randolph Cock and NAM Rodger, 2nd edition, 2008.
http://centres.exeter.ac.uk/cmhs/naval_records/

Also, for background information,
"French Prisoners of War in Britain, 1756-1815", Francis Abell, Oxford University Press, 1914.
http://www.archive.org/stream/prisonersofwarin00abeluoft/pri...

Finally, "Napoleon's Lost Legions: French Prisoners of War in Britain, 1803-1814", Daly, G, History: Journal of the Historical Association, 89, (3) pp. 361-80. ISSN 0018-2648 (2004).
I recently requested a copy of this item from ecite.utas.edu.au.
Whilst this draws heavily on the above "French Prisoners of War in Britain...", it does add a number of other references and potential channels of investigation. For example, when discussing the unions between French officers on parole at Ashby and British women, I found the following, "The British government paid for the subsistence of the wives and any children." Sadly this statement is not provided with a supporting reference. Whether this was specifically for wives and children of PoW, or whether it was part of the bastardy relief I have yet to determine. (I have found a number of contemporary accounts where such couples were advised that any marriage between them may not be recognised).

I hope the above is of interest and wish you good luck with your research.