When studying the laws of Pesach, it’s always good to start with which are the Torah laws and give them top priority.
Regarding חמץ, there are actually three Torah laws. The first is תשביתו שאור מבתיכם, to remove Chametz from our possession. We do this, according to the Torah, by making a declaration of ביטול, nullification. The Rabbis insisted on checking every place where Chametz could have entered.
The Torah also forbids us to see and find, בל יראה ובל ימצא. This applies to Chametz we own but did not nullify.
At the Seder, we have two Torah commandments. The first is to eat a כזית of Matzah. And the second is to tell the Pesach story. This is learned from the words, והגדת לבנך, and you shall tell your children.
For this reason, the children are the most important people at the Seder, and we must do everything possible to keep them involved.
The rest of what we do is rabbinic. And remember, dirt is not Chametz!