Problem solved! Emailed one of the rescues on cozietosies list and they had four 8 week old kittens whose mother was killed on the road when they were 5 weeks. Two black and two black and white - apparently black/black and white cats are hard to place at the moment as they aren't fashionable just now .
So I currently have two slightly nervous balls of fluff gamboling around the room. I'd forgotten how bonkers kittens are!
I take your point about an older cat but I think it likely (with luck) this will be our only cat for DS's childhood and I do feel the need to give him a "kitten" experience not just a cat. Will probably be constrained by what shelters have to offer anyway!
Appreciate that you want DS to bond with a kitten but remember that this one will be new to everybody and taking on a slightly older cat will mean that you not only have a steadier animal but also help out the rescues who are bursting at the seams with unwanted cats.
Best of luck whatever you decide.
PS - As to the railway line, I don't know. You'd best ask when you get in touch if it's going to be an outdoors cat.
My lovely cat was PTS last week after developing kidney failure. I miss him so much and whilst I don't want to replace him (of course because he is irreplaceable!) I hate the house without a cat (or two) in it.
Personally I wouldn't mind a young cat but DS has never had a kitten and my cats weren't really his (IYSWIM) so I would like him to have a kitten to bond with. Although he is only 7, he is a fairly calm 7 year old and is quite used to cats.
I have emailed Hounslow Animal Welfare society and waiting to hear back, would consider Battersea (though I need to go in person to apply and can't do that until at least Wednesday).
Are rescues likely to object to the fact that I live by a railway line? I really don't want to go the Gumtree/private sale route - I don't want to encourage people not to have their cats neutered. I would consider a pair if it helps.
Any other suggestions in the SOuth West London area?