Comparing to 小, 少 contains an extra 丿at the bottom. What is its meaning? Let us check its evolution history to get some clue. (screenshot taken from http://chinese-linguipedia.org)
Learn one Chinese Character a day - 少
As we can see that Oracle Script of 少 - is actually same as that of 小. They were same character when they were created! As time passed, three dots - , which becomes 小, is used more to mean Small, while four dots - , which becomes少, is used more to mean Smaller or Less. As 少 was created same as 小 originally, 少 can mean Small too.
Let us enjoy a Chinese calligraphy with 少 inside:
As and are used to present abstract meaning like small, less and etc, how would Chinese ancestors create another character to mean sand then?