1) Your question is asked by Rav Chaim Kanievsky shlit'a, in his book Nachal Eitan (3:1:17) on the laws of Eglah Arufah. First, it should be pointed out that the Me'iri here writes explicilty that if the corpse was a minor, one brings an Eglah Arufah. However, Rav Chaim adds that he heard from his father, the Steipler Gaon zt'l, that a Cheresh or Shoteh are considered "Bnei Mitzvah" and receive a reward for performing Mitzvos even though they are not obligated. In other words if the Cheresh or Shoteh perform a Mitzvah, it is considered a Mitzvah, but the Torah is not able to obligate them since they would not always be capable of fulfilling it. The Nachal Eitan writes that they are capable of doing Chesed and similar Mitzvos. So this applies even without having to apply the Sevara that they may later be healed.

2) The Nachal Eitan cites a proof for the above from the Mishnah Berurah (OC 266:14) who cites the authorities who rule that even though a Cheresh and Shoteh are not commanded to rest on Shabbos, nevertheless one is not allowed to give work to them to do on Shabbos.

3) We may suggest another source for the above ideas from the first Mishnah in Maseches Chulin 2a, which tells us that if a Cheresh, Shoteh, or minor slaughtered an animal and knowledgeable onlookers saw that they did the job properly, one may eat the meat. This suggests that they have a part in the Mitzvah of Shechitah. If a robot slaughtered an animal one may not eat it, because a robot has no Mitzvah.

4) Of course, all of the above is very relevant for special education children and similar situations. Even though they may not be obligated to do Mitzvos, what they do is considered a Mitzvah.

Kol Tuv,

Dovid Bloom

Here are more sources to show this important idea that Cheresh, Shoteh, and Katan are involved with, and able to perform, Mitzvos.

1) The first source is a surprising statement of the Minchas Chinuch. (I must confess that when my Chavrusa first told me about this Minchas Chinuch, I yelled at him and said it is impossible that the Minchas Chinuch could say such a thing, but then we looked it up and saw it in black and white!)

With Pesach only a few days away, this topic is timely. The question is: who is eligible to be part of the group which slaughters and eats the Pesach offering? The verse states, "And every purchased servant of a man, you shall circumcise him, then he may eat the Korban Pesach" (Shemos 12:44). Rashi explains that this means that the master may eat the Korban Pesach only if all of his servants have been circumcised.

The Mechilta states that when the verse says the "servant of a man," it comes to exclude the servant of a minor. That is, if a minor possesses uncircumcised servants, this does not prevent the minor from eating the Korban. The Minchas Chinuch (Mitzvah 17:14 writes that if it would not have been for this special verse, the fact that the minor possessed such servants would have stopped him from eating the Pesach. How could this be? A Katan is not warned by the Torah to circumcise his servants, since a Katan is not a "Ben Mitzvah"!

The Minchas Chinuch writes that in fact a minor is a Ben Mitzvah. However, one cannot say that the Torah warned him about Mitzvos because he does not possess "Da'as," intelligence, but a Katan is obligated in Mitzvos. The Minchas Chinuch writes that the proof for this is the fact that one is not allowed to give forbidden foods to a Cheresh, Shoteh, and Katan.

2) We can explain the last idea above with the help of the Gemara in Kidushin 39b that teaches that if a person sat still and did not commit a transgression, he receives a reward as if he did a Mitzvah.

According to this, when the Cheresh, Shoteh, or Katan does not eat Tereifah food, he is rewarded for this. This means that he is included in the Mitzvah of eating kosher food.

3) Another very important source that a Cheresh and a Shoteh are Bnei Mitzvos is from the first chapter of Shulchan Aruch, Even ha'Ezer, which deals with the Mitzvah of being fruitful and multiplying. The Rema there (1:6) rules that if somebody bore a child who is a Shoteh or Cheresh, this counts towards the Mitzvah of Peru u'Revu. The source for this is the Teshuvos Maharil #196, cited by the Beis Yosef there. One of the reasons cited for this by the Beis Yosef is that a Cheresh or Shoteh is also a Ben Mitzvah.

4) I think that, Baruch Hash-m, we have seen a few sources which suggest that a Cheresh, Shoteh, v'Katan are also Bnei Mitzvos, so Rebbi Yochanan ben Shaul will say that the Eglah Arufah must be brought to atone for their killing, since their death prevented them from doing Mitzvos.

Chag Kasher v'Same'ach

Dovid Bloom