I thought I'd share two books though today that will make you smile and which offer a myriad of avenues for getting very young children to look closely at feelings, theirs and others'. Both are by European authors and illustrators but available in English. Both appear simple because of their minimal text but they are deceptive and thus somewhat ageless.
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In My Heart: A Book of Feelings by Jo Witek and Christine Roussey. This cover illustration doesn't do this book justice. It has beautiful die-cut pages which show the heart decreasing in size. I haven't seen the original French version of this book.
Happy birthday Olivier Dunrea. His series about Gossie is ideal for preschoolers and talking about feelings too.