If a child under the age of bar or bat mitzvah is performing the mitzvah of tevilat keilim, immersing vessels in a mikvah, the halachah regarding metal vessels is as follows: If the child immerses the vessels in the presence of an adult, the tevilah is valid, and the child can make the blessing. However, one may not have a child immerse the vessels on his own, since the testimony of a minor, even of a precocious child, is halachically unacceptable. Thus, one should not trust the child’s word that they performed the tevilah correctly.
Whereas when toiveling glass vessels, for which the obligation is only rabbinic, or plastic vessels—for those who are stringent and treat them as they do glass vessels—one is permitted to have a child toivel them, and we trust the child that they actually toiveled the vessels properly.
Rav Yosef Yeshaya Braun, member of the Bet Din of Crown Heights; 1 Minute Halacha, reprinted from crownheightsconnect.com
