You already met 小 — three scattered grains. 少 takes that same picture and adds one long stroke sweeping through it, as if a grain has slipped free of the pile: not just small anymore, but fewer. That single extra line is the whole difference between "small" and "few" in Chinese writing.
A piece of culture
Liang Qichao's Young China In 1900, reformer and journalist Liang Qichao wrote a fiery essay called 少年中国说 ("On Young China"), arguing that a nation's fate rests on its youth: "少年智则国智，少年强则国强" — "when the young are wise, the nation is wise; when the young are strong, the nation is strong." Written as China faced foreign invasion and calls for reform, the essay is still memorized by schoolchildren today, and 少年 (shàonián, "the young") remains the word for that hopeful, unfinished stretch between childhood and adulthood.
Use it in a real word
少见
shǎojiàn · siu2 gin3
rare, seldom seen — literally "little seen"; you already know 见