The theme of the story "Guess how much I love you" is about love. The story is about a pair of nutbrown hare, the father and the son.
The little nutbrown hare makes the question "Guess how much I love you" to the big nutbrown hare, he shows him a proof of his love and then the big nutbrown hare makes the same question to his son, then is turn to the little nutbrown hare to shows his father how much he loves him.
The story keeps showing us all the proofs that both characters make to show how much they love each other.