“You shall count seven weeks. Begin to count the seven weeks from the time the sickle is first put to the standing grain. Then you shall keep the Feast of Weeks to the LORDyour God with the tribute of a freewill offering from your hand, which you shall give as the LORD your God blesses you. And you shall rejoice before the LORD your God, you and your son and your daughter, your male servant and your female servant, the Levite who is within your towns, the sojourner, the fatherless, and the widow who are among you, at the place that the LORD your God will choose, to make his name dwell there. You shall remember that you were a slave in Egypt; and you shall be careful to observe these statutes.

“You shall keep the Feast of Booths seven days, when you have gathered in the produce from your threshing floor and your winepress. You shall rejoice in your feast, you and your son and your daughter, your male servant and your female servant, the Levite, the sojourner, the fatherless, and the widow who are within your towns. For seven days you shall keep the feast to the LORD your God at the place that the LORD will choose, because the LORD your God will bless you in all your produce and in all the work of your hands, so that you will be altogether joyful.

So what about those too young to remember?

And your little ones who are weaned, your son or your daughter, but who are not yet able to remember that you were a slave in Egypt; they must not eat of my feast. They must be made to watch you as you eat and drink and are altogether joyful. But when they are older, and they have understood your teaching, you must bring them before the Levite and the elders in the gate and they will question him. If your son or your daughter can show that he loves the LORD your God and trusts in him, and that he is grateful for being brought out of Egypt, out of the house of bondage, then the elders and Levites at the gate can declare them worthy of my feasts.

That passage is nowhere in the Bible. We just do it anyway. Here’s a passage that is in the Bible:

And he said to them, “Well did Isaiah prophesy of you hypocrites, as it is written,

“‘This people honors me with their lips,
but their heart is far from me;
in vain do they worship me,
teaching as doctrines the commandments of men.’

You leave the commandment of God and hold to the tradition of men.”

And he said to them, “You have a fine way of rejecting the commandment of God in order to establish your tradition!”