The reason why your house was painted with a flat paint is because flat paints hide imperfections in the walls and ceilngs best. The fewer glitches people notice, the fewer complaints the contractor has to deal with.
The higher the gloss of the paint, the easier it is to clean. However, good "scrubbability" (yes, that is a real word) in paint requires that the paint have BOTH a binder that dries to a strong and hard film, and that the extender pigments in the paint (which are flattening agents and serve to lower the gloss of the paint) be made from a HARD material. Typically, the better and best paints will use various forms of silica (which is ground up silica sand) as the extender pigment. Inexpensive paints will use Talc or Chaulk as the extender pigment, and both are very soft materials. So, look for top-of-the-line paints that use silica as the extender pigment.
I'd opt for a satin in your house. It's smooth enough to allow for easy cleaning, but it's not so glossy as to make your house look like a hospital.
Better quality paints will use Plexiglas as the binder (or continuous plastic film). Plexiglas is unaffected by acids, weak solvents like paint thinner, bleach or even strong alkalis like oven cleaner. So, if push comes to shove, you can use these to clean your painted walls.
In daughter's room, you should be aware that the BEST product I've ever come across for cleaning marks and dirt off of paint is the Mr. Clean Magic Eraser. (And, I own a small apartment block, so I do more cleaning than most.) It is a foam made from a very hard plastic that has a microstructure that really doesn't resemble anything familiar. A micrograph of the microstructure of the Magic Eraser can be found in this PDF file:
http://www.corporate.basf.com/basfco...EbbMCqebbcp*2g
Those tiny things the stuff is made of, which are far too small to be visible to the eye, get into the smallest indentations on a surface to clean the dirt out of them. Stock up on Magic Erasers at your local grocery store, and daughter's love of dirt and crayons on walls won't be a problem for you. But, be warned that the plastic Magic Erasers are made of is actually quite hard, and you can scrub off the paint from the wall by scrubbing too aggressively with them. Best a light touch.
And, because you know that acrylic paints are unaffected by acids, alkalis and weak solvents, you can dip your Magic Eraser in these to aid in cleaning the most stubborn marks off, and relatively easily too.
Google BASF Basotect foam to learn more about the chemistry and microstructure of Magic Erasers.
Wood shrinks as it dries. By far the most shrinkage is across the grain, but there is still about 1/10 of 1 percent shrinkage along the grain. This is the probable reason why you're seeing tiny cracks in the paint film on your wood moldings in corners.
In all 22 of my bathrooms, I use Zinsser's PermaWhite Bathroom paint, and all 22 bathrooms are clean and free of mildew for the past 20 years. You can buy this paint at most home centers.
Stay away from adding mildewcides to paint at the point of sale. Mildewcide has to leach out of the paint at the slowest possible rate to remain 100% effective to be effective for the longest possible time. Getting the right mildewcide for the right kind of paint binder is very much a trial-and-error process. Throwing a bag of Mildex into a can of paint before shaking it is very much a shot in the dark. You're better off going with a paint meant for bathrooms where the amount and kind of mildewcide has been optimized for the gloss level and binder in the paint.