Translation:My son took a dessert from the box.
Interesting discussion on sweet, candy and dessert. My version of DL gave dessert as the only choice for dolce in this sentence. In UK English, a sweet can be either a candy (though rarely called candy) or a dessert. Or even a caramel for a specific type of sweet ( candy). A pudding is an alternative word for some types of dessert, but you can also have non sweet puddings like black or Yorkshire puddings.
I don't understand "ha preso". If the infinitive is prendere, shouldn't this be ha prenduto? Nothing in tool tips to make prendere into preso by dropping everything after pre and add an -so. Honestly I don't even know how to look up this question of mine in other resources.
I find a lot of help from this site - it has all the verb conjugations, etc. https://www.collinsdictionary.com/dictionary/italian-english