You know the Druidcraft cantrip and the Faerie Fire spell with this trait. 

Fairies also possess an innate ability to shift between their natural, small size and that of a medium humanoid as a bonus action on their turn. These sizes can persist inside of, and outside of combat. 

Natural:

‘Small.’ 65-100

Enlarged:

‘Medium.’ 130 – 180

((Last updated: 7.25.2024))