Here in the U.S., Doctor Who costumes are largely a do-it-yourself affair, particularly for children. When I decided to put together a role play outfit for my son of his favorite Doctor (Ten), I wasn't sure where to start.
Fortunately, to create costumes for two of the most popular Doctors, normal clothing can be used for the most part. Our children may already have some of what they need in their closets; local thrift stores can usually help with much of the rest. I'll include Amazon products, where available, for your convenience.
It's not at all uncommon for girls to to portray the Doctors themselves (Quirky, brainy hero who saves the universe? Why not?!), but that's not a little girl's only choice. Amy Pond, too, is handily normal in the basics of her outfits, giving us another easy costume to put together for little Whovians.