It's a tad difficult seeing as I don't know how old they are but anyways:
For your daughter:
http://www.letterbox.co.uk/
There's some really sweet stuff, good for dolly type things. They also have a catalogue. I still have one of their hairbrushes from when i was 4 o_o
http://www.katzwhiskas.co.uk/
If she's into Hello Kitty, as I once was, this website is great for things you can order in the uk, I'd go for something like the scarf [nice and cosy and she can wear it on the day]
For your son:
http://www.amazon.co.uk/exec/obidos/...111734-1387062
http://www.amazon.co.uk/exec/obidos/...111734-1387062
He probably wants the newer furby, with
kerazy colours, 6 times more memory and some spoon-type thing, god knows why.
http://www.amazon.co.uk/exec/obidos/...111734-1387062
If by toy camera do you mean, the real deal 4 year old toy camera,
with plastic bits that snap off, then this should be about right.
http://www.amazon.co.uk/exec/obidos/...111734-1387062
This looks good for 'games'.
http://www.amazon.co.uk/exec/obidos/...111734-1387062
Or this one if he's younger. Heehee,crunching crocodile.
Hmm, hope that helps, just say more stuff they like and I'm sure we could come up with some more things.