Baby-pants.com - sells diapers, onesies, footy pajamas, bibs, and shirts; boys, girls, and gender neutral clothing.
cosyndry.com - sells diapers, sissy clothing, onesies, rompers, shoes, and accessories; boys, girls, and gender neutral clothing
Starryideas.net - cloth diapers, overalls, rompers, diaper covers, bibs, dresses, etc.; boys, girls, and gender neutral clothing
MinasABplace - rompers, dresses, accessories, and bibs; a couple gender neutral stuff (there’s an adorable Pokemon bib) but mainly girly items.
ForeverABaby - rompers, bibs, diaper covers; gender neutral clothing.
MyBinkiesAndBows - Dresses
ABUniverse.com - diapers (lots and lots of choices) and clothing; boys, girls, and gender neutral items.
ForeverAKid.com - dresses, pajamas, bloomers; boy and girl items
PinklyEverAfter - Imouto kei and fairy kei items (super cute but not cheap); bloomers, dresses, tutus, accessories; girl items
PetticoatsByLori - Petticoats/tutus
SpreePicky - Cute J-fashion, school girl outfits, Sailor Moon items, Maid dresses, lolita fashion, wigs, accessories
Ink and Ponies - Cute accessories and t-shirts
CottonsSmallCloset - J-fashion and lots of cute girly clothes
90s Jelly Sandals
PlusCuties - Plus size friendly with lots of cute clothes!
Showishes - Another shopping service like Spree Picky with similar content.
I browsed through Etsy and Storenvy for cutey stuff that I see littles reblog. You can find these and a lot more (you’ll see when I do an accessories post) by searching through tags like “fairy kei”, “lolita”, and “j-fashion”.