This weekend we took a trip down to Brighton to visit friends, they took us to loads of good shops where I could easily have filled the car with second hand clobber. One place we stopped at, Dinky Vintage, has a great collection of children's clothes for sale and to rent with excellent condition stock from the 30's through to the 70's. The clothes are all reasonably priced, particularly considering how hard it is to find such good condition and sometimes unworn, period kids clothes.
Apparently there's a website on the way, I'll link to it as soon as it's up.