in general,it means"all kinds of "or"diverse" instead just "big and small ones".
why are the characters doubled? cuz it's a fixed expression,there are many other AABB words or phrases,too.such as 干干净净,漂漂亮亮,兢兢业业(hard-working)明明白白,家家户户. i think it is to emphasize and exaggerate the emotion and affection when they are doubled.
hope it will help:)