Take advantage of naptime to do your paperwork. Schedule a half an hour of book time for your charges. Have them look at books while you are catching up on important paperwork. Let them learn a little science by quietly blowing bubbles and watching them, as you write. Tell them to do this quietly, but to think of questions to ask you about bubbles.
Free play is important for young children, also.
It may not be as quiet, but it is educational and does not require your direct involvement. Give them half an hour of free playtime with blocks, dress up clothes, and other toys. This allows your charges to work on fine and gross motor skills, social skills, language skills, and more. Sit nearby, so that you can oversee their play, as you do your work. Remind them not to eat the shaving creme or to wipe their eyes when playing in it.