I wouldn't wash them! They might catch a cold at that young age and their preening skills are not yet developed.
As adults they LOVE a bath of spray with a water bottle (I use the hose pipe on gently and mine will sit for hours under the sprinkler!) but as a baby i used cotton wool pads soaked and gently squeezed out with warm water (not to hot or you may burn them) and wipe them down. I wiped the face after every feed because she neded up with formula everywhere and around the bum if need be but try not to "soak" the bird, just wipe.
Food around the face can go hard and rot and I found that the luke warm water gentle lossened it and never made her too wet.
As an adult now, after her "bath" with the hose or bottle i make sure she gets some sun (not too much) and stays out the draft. She will preen herself as an adult and get dry in no time - a baby doesnt have those skills. So stick with the warm water and cotton wool or a soft cloth
it's important to keep them clean at that age
