The word little can be used in two different senses--meaning "small in size" or "small amount of."
Examples: He was still a little boy. (small in size)
Please give me a little milk. (small amount of)
This becomes trickier in the comparative and superlative because little has two different forms.
If little means "small in size," the comparative is littler or more little, and the superlative is littlest.
If little means "small amount of," the comparative is less, and the superlative is least.
Examples: He was the littlest boy in the class.
Please give me less milk than he has.
He drank the least amount of milk of anyone there.
See also Irregular Comparisons.