I'm afraid this is where the hard bit starts!
Births, marriages and deaths prior to 1837 were recorded in the Parish Registers of the local church, following a christening, marriage or funeral - so births as such were not recorded - only christenings.
You will need to work out which parish they lived in then go to the local record office (or county archive) to look at the registers, which are usually on microfilm.
(This presumes they were Church of England, of course, if they were any other religion your search will be a little trickier!)
You could also search online on the IGI site (
www.familysearch.org) which will give you a guide, but these records aren't fool-proof.
Happy hunting!
Chris