I used to do it all the time when we went out. If I liked something & it was in both sizes I bought it. If not I'd find something else.
These days DD1 would shoot me, but every time I buy them something they winge that the other got the 'better' one, so I try to get everything similar, but not the same iykwim. The same but different colours or something.
I personally think they look so cute dressed the same when they are little