"You are small."
Translation:Vy jste malé.
It's not wrong, it's just weird.
Although "(Ty) jsi malé" is grammatically correct when said to a child, it's much more natural to say "(Ty) jsi malý/malá" depending on whether you're talking to a boy or a girl.
However, if you add a noun, it becomes natural: "Jsi malé dítě." (You're a small child.) or "Jsi malé kotě." (You're a small kitten.)
That is also acceptable. The "VY" here can mean many things. You a male i am talking to, you a female, you an it (a child), VY a group of males or VY a group of females.
The one in the "main! translation is me addressing a group of females.
Vy jste malý = single male, formal addressing Vy jste malá = single female, formal Vy jste malé = single neutral formal or multiple female only group Vy jste malí = multiple male or mixed group