I will say that my DDs preschool teachers did an awesome job of keeping the kiddos clean and using appropriate paint smocks etc. My oldest was and is a very neat child. Because I have 2 girls, I started spending more on her outfits knowing they would get worn by both, and then hoped for some resale value. Of course that turned around and bit me in the behind.
DD#2 was anything but neat, she has earned her nickname of "the mess monster". If there is a molecule of dirt in the air, it will find its way onto the front of her shirt. A lot of her stuff, especially shirts, end up with a variety of stains. Most of the time they are faint and she continues to wear the shirts, but every now and again there is a whopper I can't get out and the shirt is trashed. Kindergarten and chocolate milk every day for lunch was the worst year.
so buy inexpensive stuff for school that is still cute. I like Target and Children's Place for playclothes. I also shop garage sales and consignment stores for nicer brands and a good price. Gymboree was "the good stuff" for me, but some people consider that playwear and use boutique labels for nicer occasions. It all depends on your price point.