Ordinary Mary's Extraordinary Deed is a tribute to random acts of kindness and the chains of positive events that can start with something very small. Written by Emily Pearson and illustrated by Fumi Kosaka, this book is a nice read-aloud for preschool-aged kids. They'll enjoy the bright, primary-colored illustrations and the interesting set of characters that influence the friends and strangers around them.
Sometimes I've found that when kids aren't sharing well, or when they're overtired, they just need a reminder about the power that is in them to influence others. Frankly, we all need that reminder from time to time. Reading a story like this one will help to re-set your kids' outlooks and get them back on track.