Mud by Mary Lyn Ray and Lauren Stringer

Age group:  3-6 (reccomendation from Toddlers who are 2-3)
Now that winter has melted away, this book speaks to what children have been experiencing outside - mucky, gooey mud.  Since they all enjoy mud, they are able to bring their personal experiences to the story while learning why there is mud after winter.  The illustrations capture the essence of mud which immediately attracts the children.