Midrasch zu Schemot 12:10

And the people took their dough before it was leavened … upon their shoulders (Exod. 12:34). This indicates that the dough did not have sufficient time in which to leaven. Similarly, concerning the Messianic days, it states: Who ceaseth to stir from the kneading of the dough until it be leavened (Hos. 7:4). Their kneading troughs (mish’arotam), alludes to the leftover (shi-yu) unleavened bread and bitter herbs. You may interpret it so, but perhaps it does not refer to the remnants of the unleavened bread and bitter herbs, but to the remnants of the Passover sacrifices? However, since Scripture says of the paschal sacrifice: And ye shall let nothing of it remain until the morning (Exod. 12:10), it could not refer to the leftovers of the paschal sacrifices. Upon their shoulders (ibid., v. 34). Did they have no beasts of burden to carry the remnants of the unleavened bread and bitter herbs? After all, it is written: And a mixed multitude went up also with them; and flocks, and herds, even very much cattle (ibid., v. 38)? They did so because they cherished their religious obligations deeply. And so it is written: upon their shoulders.

One might think that the law about the phylacteries applies, likewise, to women. Hence Scripture says: That the law of the Lord may be in thy mouth (Exod. 13:9). And who are they that study the law? Men. Therefore women are exempt from so doing, for they do not devote themselves to the law. It may be possible to conclude that the law of phylacteries applies to children. Therefore Scripture says: And Thou shalt keep it; and that applies to all who are diligent in the study of the Torah and in the performance of good deeds. Hence a child is exempt. But if a child is a Bar Mitzvah or well informed, he must fulfill the law. It is possible that one may neglect to examine the phylacteries, and so Scripture says: from year to year. From this statement they conclude that a man should examine his phylacteries at least once every twelve months. From year to year is mentioned in this verse, and further on For a full year shall he have the right of redemption (Lev. 25:29) is stated. Just as in the former case a year means twelve months, so also in the latter instance a year implies twelve months. This is the opinion of the School of Hillel. The School of Shammai, however, argues: One need not examine them ever after. So Shammai said: “These are the phylacteries of my mother’s father.”