My DD is 7 and has moved beyond all the frills. She assures me daily that she's casual girl these days. Generally, she prefers to only have one piece 'Disney-ified'. If the bottom is Disney'ed, the top is a plain T, possibly with a Mickey applique in a coordinating fabric. If the top is done, we pair it with a pair of plain bermudas.
Her ongoing faves are:
Twirl skirts (you can do a minnie dot or any red/white polka dot). Beyond easy! No pattern required!
A peasant top in blue with Peter Pan characters shadowed in front of a yellow moon (DD loves her Peter Pan). Worn with plain bermuda shorts. Lots of people here can recommend ones that fit - I ended up with a Butterick.
I also like a simple dress in Minnie dot fabric - we love Butterick 4718
http://butterick.mccall.com/b4718-products-5624.php?page_id=376
Sorry, no pics...I'm on the wrong computer.
Deb