The correct option is B A little kindness is never a bad thing.
The phrase 'little kindness' emphasizes on 'little' changing the meaning to 'almost no kindness', whereas the sentence means to generate the presence of kindness, not the lack of it, hence the statement needs to be corrected. Therefore, option D is incorrect. By adding 'a' the meaning of the phrase 'little kindness' changes, where 'a little' is a positive quantifier, which means 'a small amount of', hence Option B is correct. Option A is incorrect because 'the' is meant to specify the noun, whereas the statement is a general one and the noun is also general. 'Each' is usually used for plural countable nouns since the noun 'kindness' is an uncountable, Option C is incorrect.