Hello Vpflower, welcome to UE!
It seems to me that (if we confine ourselves to the adjectival uses, and to examples where either word may be used) "small" tends to be the neutral word, whereas "little" tends to express the attitude of the speaker towards the thing described.
Compare for instance:
1. Just a small piece of cake for me, please!
2. Just a little piece of cake for me, please!
3. A small boy was staring at me through the window.
4. A little boy was staring at me through the window.
5. What small feet you have!
6. What little feet you have!
#6 seems to have an air of fondness, or amusement, for instance; whereas #5 tells us only about the feet. And "little boy" in #4 seems friendlier towards the child than #3's purely descriptive "small boy".
But that may simply be my personal interpretation. I'd be interested to hear what other posters have to say.