(Mishnah): A woman may receive a Lulav from her son or her husband and return it to water on Shabbos.

R. Yehuda: On Shabbos one may return it to water, on Yom Tov one may add water and on Chol HaMoed one may switch the water.

A child who understands how to shake is obligated in Lulav.

(Gemara): If he knows how to shake, he is obligated in Lulav.

If he knows how to wrap himself, he is obligated in Tzitzis.

If he knows how to speak, his father teaches him the language of the Torah (Hebrew).

If he knows how to keep his hands from becoming Tameh, he may be fed Terumah.

If he knows how to keep his body from becoming Tameh, he may be fed Taharos.

But he cannot lead prayers nor recite Birkas Kohanim nor stand on the platform of the Levi'im to sing in the Temple (although he may stand on the ground between the legs of the Levi'im) until his pubic hair is fully grown.

Rebbi: Even if they have fully physically matured, they must also have reach aged twenty, as the Pasuk states (Ezra 3, 8), "...they positioned the Levi'im from aged twenty and above, to direct the work of the Temple."