Q. Dear Rabbi, What happens when my daughter under bat mitzvah age ate chametz on Pesach? Is this a sin for her or for me or it doesn’t count as a sin at all. Because she is under bat mitzvah? or chas ve shalom is it karet?

Thank you Rabbi, Pesach kasher ve sameach!
　
A. Even though a minor is exempt from Mitzvos, positive and negative, if he/she has reached the age of understanding, he/she would be subject to the Mitzva of chinuch or being educated in the precepts of the Torah. This responsibility rests primarily on the parents of the child. One should be far more vigilant in prohibitions that involve eating. The reason being that we are what we consume. If we ingest non-kosher animals we assume their nature and incorporate their instincts (Ramban, Shemini). Many Poiskim suggest that the same applies to the chometz (that represents the Yetzer Hara) prohibition during Pesach even though it is time dependent, and not an intrinsic (Issur Cheftza) proscription (Arugas Habosem O.C. 138, Chinuch Yisroel 3,6 et al.) others disagree (ibid. – Shaarei Deah)

Our sages teach us in many instances, that eating wrong foods will change a child’s disposition to keeping Mitzvos, as in the cases of Acher (Tosafot Chagiga 15a), Rabbi Yochanan and Shabtai, the hoarder of produce (Yoma 82b), Rebi and Antoninus (Tosafos Avoda Zara 10b), Yochanan Kohen Gadol (Bnei Isaschar, quoting the Arizal), and many others.

Most Poiskim agree that a minor does not require any Kapara or forgiveness for sins committed while he was a minor and will not be punished for them (Rabbi Akiva Eiger – responsa 2- 134, Chavas Yair 166, Chasam Sofer E.H. 2-172, et al). However, Remah O.C. 343, and Sefer Chasidim 692, do mention some Kapara requirement. Chida (Chomas Anach – Shemini) points out that it varies with the state of understanding of the minor.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a