Searching for scifi/fantasy book series w/flying carpet transportation in Victorian era w/dragons li

Something by Mercedes Lackey? I don't remember dragons, however...
Sounds like E Nesbit as mentioned above! Phoenix and the carpet would be closest I think.
Was it about a boy in a fantasy world who went to Victorian London to get supplies to help win a battle? I can't remember the name but I think I read something like that when I was 12 or so.

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