L.F.
Hanna Andersson sometimes has matching outfits for girls and women. My friend works for Hanna Andersson, and back in the 90's, they were selling out of all of their matching outfits because Japanese moms were wanting to dress exactly the same as their daughters -- even down to the same hats or hair accessories. Their kid sizes can get quite large too, so if you are petite, you might even be able to fit into their big kid sizes.
Otherwise, you can try J.Crew/Crewcuts and Boden/Mini Boden. Good luck!