Hi Bean
The Folkestone baptisms and marriages have been transcribed (up to 1840) on
http://familysearch.org though, as any index, they are open to error.
Note:- the batch number for Folkestone is P020721.
Have your tried Penny's Folkestone site at:
http://freepages.genalogy.rootsweb.com/~folkestonefamiliesI see that she has some SLADDEN baptisms on there - but no BANKS. Why not email her about the SLADDENs - it may lead to something.
A good source for Folkestone families c1800 is the napoleonic papers 1803. These list heads of household and other able bodied males with their occupations and their duty in the likely event of evasion. It would usually give (for each household) name, age, abode and occupation of head and number of adult males (over 15 I think without looking it up), adult females and number of children (under 15?). If the family were living in Folkestone at this time, any Richard of the right age might not be listed by name as he was too young but you should be able to see how many children were in the household - maybe that would help you decide?
They may have now been published by the Folkestone & District FHS
http://www.folkfhs.org.uk/publications.htmor available at The Heritage Room, Folkestone Library, Grace Hill, Folkestone if you are interested. They do up to half an hours research for free - after that there is a charge - if I am up to date with their policy. Maybe you could get there - they have lots of "goodies" for Folkestone families.
I would say that SLADDEN is a "Folkestone" name - I have come across it many times over the years but not noted anything because it wasn't of interest to me at the time.
Were they mariners? It just might explain why they travelled from Folkestone to Cornwall - if you are on the right line. In the late 1700s there were a number of folkestone women who went to Holland to have their children - to give them dual nationality so that they couldn't be press ganged into the navy. As far as I am aware, there are no offical records of such but the story crops up now and again in reports of old smuggling cases.
Could Richard have been born before marriage? There was this, custom I suppose you could call it, in ancient Folkestone that a woman wasn't worthy of marriage until she had proved herself capable of bearing a child. Such was this local tradition, that the local curate offered a gift of a teapot to any couple marrying where the bride wasn't with child or had already had a child. I think I remember reading somewhere that it was only claimed once!
You say that Richard was born Jun 1791 LIskeard, Cornwall - may I ask where this information comes from? Did he live in Folkestone?
Hope you find this of some interest
Casalguidi