We don't use that. Instead we use "You're nice" which can be translated like "Estás bueno". Anyways you mustn't use that too much in Spanish. It sounds like you're desperate.
un niño está caliente
"gato caliente" means Hot cat in "spanish"
Say "you're hot."
You can say "¿eres un niño?"
Good boy = Chico bueno
Usted es atractiva-- you are sexy. 'hot' is food of something not person.
"amante"
papa
If you mean hot like warm, we say "chaud" If you mean a hot girl or boy we usually use the English word "sexy". So for a hot boy we say "un garçon sexy"
Hot date - fecha caliente
calor [ka'loɾ]
"Tengo calor"