The Torah speaks of four children: One is wise, one is wicked, one is simple and one does not know how to ask. …What does the wicked one say? “What is this service to you?” (The Haggadah)

כְּנֶגֶד אַרְבָּעָה בָנִים דִּבְּרָה תוֹרָה: אֶחָד חָכָם. וְאֶחָד רָשָׁע. וְאֶחָד תָּם. וְאֶחָד שֶׁאֵינוֹ יוֹדֵעַ לִשְׁאוֹל . . רָשָׁע מָה הוּא אוֹמֵר: מָה הָעֲבוֹדָה הַזֹּאת לָכֶם -הגדה של פסח

In four places, the Torah instructs us to relate the story and mitzvos of Pesach to our children. According to the Haggadah, each of the four conversations described by the Torah reflect one of four types of “children” asking the question: the wise son, the wicked son, the simple son, and the son who does not know how to ask. Notably, three of the four verses speak of the child in the singular tense, saying, “When your son asks,” or “You shall tell your son.” Only once does the Torah describe this as a conversation with multiple children, in the question attributed by the Haggadah to the wicked son: “And it will come to pass if your children say to you, ‘What is this service to you?’” (Shemos 12:26).

The reason for this is that other three questions (or lack thereof) can each be coming from only one type of child. The questions’ varying degrees of complexity clearly reflect varying degrees of academic achievement or ability; namely, a wise son, a simple son, or a son who does not even know enough to ask.

The dismissive question of, “What is this service to you,” however, is not limited to a person of any specific level of intelligence or education. This type of question stems simply from wickedness. Therefore, “children,” in the plural, pose the question of the wicked son in the Torah, because this question could be coming from many different types of people. They might be as knowledgeable as the wise son is, or as clueless as the simple son. In fact, the most scornful and dismissive tend to be those whose Jewish education and knowledge is so minimal that they truly “don’t know how to ask.”

—Igros Kodesh, vol. 2, p. 365