That's a little awkward, the size adjutsable ones usually go with sock sizes, so 9-12 or 13-3.
Why don't you want inlines? They are much easier to find size-adjustable. Depends who you ask, but most people find it easier to learn on inlines (quads are better for maneuverability).
Where are you located? Do you have a dedicated skate shop near you? For inline beginners I can easily say buy starter skates in Argos, but for quads you're better off going to a specialist shop not least because they cost more.
This sort of thing online is what you could get, but I would phone and check on the sizing (some come up quite small). You could put child in the skate with 2 pairs of socks and buy a size 1, perhaps -- a lot of people do that.
ps: any luck with the 18" bike?, I answerd you on another thread .
Thanks ragged. I know that I have had a lot of trouble with how sensitive inline skates are to slight inclines/ declines and DS1 is a sensitive soul so would be happier with something more stable I suspect. We're off on holiday tomorrow so didn't want to rush any purchases - I'll have a look around when we get back .