“…And Moshe assembled the entire community of Bnei Israel…” – Shemos 35:1

וַיַּקְהֵל משֶׁה אֶת כָּל עֲדַת בְּנֵי יִשְׂרָאֵל – שמות לה, א

Moshe assembled “the entire community of Bnei Yisrael” when he announced G-d’s command to gather the materials necessary and construct the Mishkan. According to the Ohr Hachaim, the Torah’s emphasis that Moshe assembled the entire community teaches us that Moshe assembled also the women and children for this announcement, for even children took part in contributing for the Mishkan (see also Avos D’Rabbi Nosson 11:1).

This represents a departure from the Torah’s typical expectations from children under the age of majority, who are neither required nor held accountable for the fulfillment of any of the Torah’s commands.

Why then were children included in the donation drive for the Mishkan?

One explanation for this is that the mitzvah to construct of the Mishkan was a means for Bnei Yisrael to atone for their worship of the Golden Calf (see Shelah, Vayakhel). Now the sin of idolatry is unique in that although Jewish law never holds minors accountable for their actions, nevertheless, the sin of idolatry can cause even children to be punished. We find this in the law of Ir Hanidachas, when all (or a majority) of the inhabitants of a particular city take to idolatry, in which case all residents of the city who are found guilty of worshipping idols are punished alongwith their wives and children (see Rambam, Hilchos Avodah Zarah 4:6).

We similarly find in the story of Purim that because the Heavenly decree against the Jews was because they succumbed to idolatry (according to the Talmud, Megilah 12b,) therefore the mortal decree issued by Achashveirosh was to annihilate the entire Jewish nation, “young and old, children and women” (Esther 3:13).

Accordingly, since the consequences of the sin of the Golden Calf affected all Bnei Yisrael, including children, therefore children too took part in rectifying this sin through the construction of the Mishkan.

—Likutei Sichos, vol. 3, pp. 930-931