Reference in Gemora Shabbos 133a Daf Yomi recently to tzaraas (skin disease see Leviticus 13) on the foreskin regarding mila (circumcission). This implies babies can have tzaraas.
If tzaraas is not a physical affliction, when did the baby sin in-order to be afflicted?
Surely he should have been warned -- on walls, clothes prior to body affliction?
How would a baby atone for tzaraas per instructions in Torah?
Negaim i.e Tzaraas skin disease - takes effect against our will whether we sin or not even without prior warning (despite the fact that sometimes one is warned as questioner assumes)Yalkut Shimoni Vayikra 247*
ומה נגעים שטמא בהן אנוסין*
Indeed the Gemara Nedarim 35b states that all under-aged mechusrei Kapara (those who need to bring a Korban inorder to enter the Beit Hamikdash), their father brings the atonement Korban Chatos on their behalf:
א"ר יוחנן הכל צריכין דעת חוץ ממחוסרי כפרה שהרי אדם מביא קרבן על בניו ועל בנותיו הקטנים שנאמר (ויקרא טו, לב) זאת תורת הזב בין גדול בין קטן
Ran explains that the father brings the Korban on behalf of his son who is a Metzora (leper) because he does not need daas i.e intention to become pure again:
מחוסרי כפרה - זב וזבה ומצורע ומצורעת ויולדת ובכולהו כתיב תורת וקרי להו מחוסרי כפרה משום שאסורין ליכנס למקדש ולאכול בקדשים עד שיביאו כפרתן והני כיון דאין קרבנן בא לכפרה אין צריכין דעת
*It seems that the Bavli Shabbos 133a and Nedarim 35b seem to Pasken like Rabbi Yehuda who says Tzaraas will happen whatever people do in Sifra Metzora: 5,4:
"ונתתי נגע צרעת" – אמר ר' יהודה בשורה הוא להם שבאים עליהם נגעים. ר' שמעון אומר "ונתתי נגע צרעת" – פרט לנגעי אנסים
But Rabbi Shimon says it doesn't just happen against peoples will. This could mean that they only get it as punishment e.g for Lashon Hara or Gasus Ruach Like Rabbi Meir goes on to say 5,12:
וכי מה מטמא בנגעים? הרשעים או הצדיקים? הוי אומר הרשעים
Or it could be that even Rabbi Shimon would agree Children are punished because of parents wickedness Like Gechazi's sons who were stricken because of his sin.
In the following edit of the original answer, I have tried to explain what I think @motel intended. Here is what he wrote:
"and he visits the sins of the Fathers on the children". Devarim 5:8
This is my version: it is not my view - just an attempt to reveal what he thought.
In Shemos 34 (7) the Torah says,
נֹצֵ֥ר חֶ֙סֶד֙ לָאֲלָפִ֔ים נֹשֵׂ֥א עָוֺ֛ן וָפֶ֖שַׁע וְחַטָּאָ֑ה וְנַקֵּה֙ לֹ֣א יְנַקֶּ֔ה פֹּקֵ֣ד ׀ עֲוֺ֣ן אָב֗וֹת עַל־בָּנִים֙ וְעַל־בְּנֵ֣י בָנִ֔ים עַל־שִׁלֵּשִׁ֖ים וְעַל־רִבֵּעִֽים׃
extending kindness to the thousandth generation, forgiving iniquity, transgression, and sin—yet not remitting all punishment, but visiting the iniquity of parents upon children and children’s children, upon the third and fourth generations.”
The Chizkuni understands this to mean (from Sefaria)
He therefore imposes partial punishment, delaying the balance if the sinner does not repent, or forgiving the penitent sinner by delaying the unexpired guilt indefinitely. He therefore exacts that part from the third or fourth generation of the original sinner. [This is not unfair, as if the original sinner had received his entire punishment, the grandson would never have seen the light of day. Ed.]
The Tzaraas on the baby is an example of this.
