Dear Rabbi, in my Siddur (Artscroll), in the bracha ’Shma Kolenu’ there is an insert that starts with אנא ה" חטאתי... מיום היותי על האדמה עד היום הזה My question is: why ’מיום היותי’ (translated in the Artscroll siddur as ’from the day I have existed’)? When someone is a baby, how can he sin? what is the chet of a baby? Or does the text mean something in the sense of ’between my birth and this day’ (i.e. in my lifetime until this day)? Thank you in advance!

Good point! The prayer in question is clearly not essential and not even found in most siddurs. Its wording is not from chazal, so its problematic nature shouldn’t really bother us (in general, I don’t recommend Artscroll, nor their translations). It is found in the Kolbo (relatively recent, as far as prayers go), and the intention is clearly as you suggested, “I have sinned in my lifetime”. The wording is loosely borrowed from Shmot 10, 6, but has nothing to do with this context. I personally don’t say this paragraph, but if you wish to do so, being that prayer is serious and should be worded precisely, I suggest omitting that inaccurate phrase, whose originality is questionable, and you can just say "בחיי" (=”in my lifetime”, for it’s also possible that one didn’t sin today).