Formal:
* "De doux rêves à vous aussi." (This is the most literal translation and is appropriate for someone you don't know very well.)
Informal:
* "Fais de beaux rêves toi aussi." (This is more casual and can be used with friends or family.)
* "Bonne nuit et fais de beaux rêves." (This is a good option for someone you're close to.)
* "Dors bien et fais de beaux rêves." (This is another common way to say "sweet dreams" in French.)
Affectionate:
* "Fais de beaux rêves mon/ma [name/nickname]." (This is a sweet way to say "sweet dreams" to someone you love.)
No matter which phrase you choose, remember to say it with a smile!