סנהדרין נה:
"רחמנא הוא דחס עלויה, ברכת ברוך שפטרני"
The Mishnah gives 2 reasons why if someone does an עבירה with an animal [הבא על הבהמה] the animal is also stoned. 1. Since a תקלה, downfall [מכשול עון] happened with it, it is stoned. 2. So people shouldn’t say this is the animal that caused פלוני to be stoned. ר' המנונא asks: are both reasons necessary to be applicable for the animal to be stoned? If the person was a שוגג, there would be קלון (degradation) by people later recognizing the animal, but there is no תקלה, as this person was a שוגג? The Gemara attempts to answer from a Mishnah: Aבן תשע שנים ויום אחד that sins with an animal, although the minor isn’t killed, the animal is stoned. We see from here that קלון is enough to kill the animal, because תקלה is not relevant as the קטן is not a בר עונשין & there is no מכשול עון. The Gemara says this is not a proof because since the קטן was a מזיד there is a תקלה, just the Torah has pity on him as he is too young to be held accountable. למסקנא, we pasken, if a גדול is בא על הבהמה בשוגג the animal is not נסקל. But if a קטן does the same thing במזיד, it will get stoned, עיין תוס' רע"א.
This concept needs explanation. If a קטן is not a בר עונשין why is his עבירה considered a תקלה? [קובץ הערות ס' עה, אות ב'] ר' אלחנן explains, that which is אסור to a גדול is ראוי to also be אסור to a קטן, just that a minor is not a בר אזהרה but the "סיבת האיסור" is there, that’s why there is a תקלה, but there is no "איסור בפועל" because he’s אי אפשר להזהירו. [שו"ת תניינא ס' קלד] רע"א explains, even though in general we are not מחוייב להפרישו if we see a קטן doing איסורים, still this is considered a תקלה because the קטן did it במזיד) "בשאט נפשו") which if done when he is a גדול will be an עבירה. The [או"ח שמג] רמ"א says there is a ענין if one was עובר עבירות when he was a קטן, when he becomes a גדול, he accepts upon himself to do תשובה even though his transgressions occurred when he was a קטן. The מגן אברהם [ד] says, this is consistent with our Gemara that says when a קטן does an עבירה although there is no קלון, there is a תקלה. The רמ"א [או"ח רכ"ה,ב] brings a י"א that when a son becomes בר מצוה, his father should recite,"בא"י אמ"ה שפטרני מענשו שלזה" . It is best to make this bracha without שם ומלכות.The משנ"ב brings the מגן אברהם that explains the reason for this bracha is because until now the father was נענש when his son did עבירות because he wasn’t מחנך him properly. However, now that the son is a גדול, he is responsible to be מחזק himself to be מקיים מצות ה'. [ח"א ס' ד'] שו"ת דברי מלכיאל explains that the יסוד of ברוך שפטרני is like ברכת הגומל which is a ברכת הודאה that we make in front of a מנין. This is why חז"ל were קובע that ברכת הגומל is made by קריה"ת, so too, ברוך שפטרני is made בשעת קריה"ת. [אג"מ יו"ד ח"ג ס' יד' אות ד'] ר' משה explains that a בר מצוה does not make a שהחיינו because a שהחיינו is made on a חדוש חיוב המצוה, but not when the time to do the מצוה has arrived because of the גברא. Since the חיוב is here because of קבלת התורה, even the קטנים are included in this קבלת התורה, because our forefathers accepted it for דורי דורות.