No I don't have my own lo's, but I know there are lots of families who do - and they say it is a really positive experience for everyone, their kids learn a lot about about disabilities and enjoy sharing with another child.
I think the social worker who does your assessment would look into how it could impact on your family, and if you go ahead they would 'match' you carefully with a child who would fit in with your family.
Me and my partner have just been approved as short break foster carers. We applied to essex council and had to go through the same process as people wanting to be full time foster carers! It's a lot of work but we have just been matched with a family and will now provide respite for a weekend every month!!! Normally the children who get short breaks have disabilities. Hope that helps! :-)