The Gemara 2b states,according to Raba bar Ulla, that any impure person who slaughters and then says that he is certain that he did not touch the flesh of the animal is believed and the Shechitah is Kosher, with the exception of a Cheresh, Shoteh and Katan, because we are worried that the latter may have committed some basic error concerning the laws of Shechitah.

The Gemara then explains that according to this, when the Mishnah teaches that "v'Kulan she'Shachtu v'Acherim Ro'in" this cannot be referring to Cheresh, Shoteh v'Katan because if so the Mishnah should not have said "And all that slaughtered" but rather "And if they slaughtered" since we had just been referring to Cheresh, Shoteh v'Katan. The Gemara therefore concludes that 'v'Kulan she'Shachtu" must be referring only to an impure person who slaughtered a holy animal and is no longer available to be asked if he touched it. Since others saw him doing the Shechitah we assume it was in order.

Therefore "v'Kulan she'Shachtu" does not include Cheresh, Shoteh v'Katan, not because in principle it would not be in order if others had observed that they performed the Shechitah correctly, because actually this would be sufficient. Rather, the words "And all that slaughtered" would not be an appropriate phrase to use but instead the Mishnah should have said "and if they slaughtered" if it was referring to the Cheresh, Shoteh v'Katan who had just been mentioned.

Kesivah u'Chasimah Tovah,

Dovid Bloom