9 and 5 here and they have been doing this since about 3. I've never had any problems though. I love their own individual style.

The only time I step in is if it's summer clothing in winter or vice versa, but then all I say is warmer/cooler top/shoes/pants etc.

DS has his OWN style for sure. He will not wear matching socks, unless they are school socks. Refuses to wear matching PJ's. And has to wear a singlet under his flannel pj top because he has to wear the top open o_O I don't get it. Never have. And whats worse is none of us dress this way, it's purely his own creation lol.

DD is actually a fashionista. She picks her own clothes way better than I would dress her, I don't know where she gets it from but she's definitely got an eye for fashion. So she's never really been a problem.