Learn Farsi: شیطنت این پسر همیشه پرستار را می‌خنداند. - This boy's naughtiness always makes the caregiver laugh.

The basic verb is خندیدن (to laugh), and its present stem is خند. To make it causative (meaning 'to make someone laugh'), we add ان to that present stem, giving us خندان. Finally, we build the present tense normally by adding the prefix می and the 'he/she/it' ending د to form می‌خنداند.

Why does پرستار (caregiver) have the direct object marker را after it?

When you change a verb from 'doing' an action to 'making someone do' it, the person being made to do it becomes the direct object of the sentence. The naughtiness is causing the caregiver to laugh, so the caregiver receives the action. Because پرستار is a specific person, it must be followed by the direct object marker را.

How do we link the words to mean 'this boy's naughtiness'?

You use the Ezafe! You take the noun شیطنت (naughtiness), attach an unseen 'e' sound to the end of it, and follow it with the possessor این پسر (this boy). It is pronounced 'sheytanat-e in pesar'.

Is the word شیطنت (naughtiness) related to the English word 'Satan'?

Yes, they come from the same ancient root! In Farsi, the word شیطان means the devil, but when used for children it simply means 'naughty' or 'mischievous'. The word in this sentence, شیطنت, is the noun form, meaning 'mischief' or 'naughtiness'.