Ok, what it seems to boil down to is if things were as bad as you say the U.N. would be interfering. Why isn't the U.N. stepping in to protect human rights. Since you are pointing out this violation to human rights that I was unaware of. I would like to point out this other violation of human rights I can't seem to get many people on board with.

European countries have outlawed spanking have legally redefined parental autonomy to a child's right to protection and non-violent upbringing. Even psychological injuries are not allowed. The law holds parents as authority in education, health, and daily routines. But the law treats the child as an individual citizen with the same basic human rights as an adult. I think America should put this law into force. The law should treat children as individual citizens. Here is some articles I found that show some merit to what I am saying. I don't think spanking should be allowed on children.

According to Whitfield M.D. 80 to 90% of families are dysfunctional. According to https://www.fox2detroit.com/news/spanking-can-pose-long-term-harms-to-children-5-decade-analysis-suggests show As many as 80 percent of parents worldwide spank their children, according to a 2014 UNICEF report. ( sorry I couldn't find a more recent survey of parents who spank)

https://www.bbc.com/news/articles/c2eyke83yz9o It observed that those who had been smacked saw the likelihood of them failing to get five pass grades (A*-C) at GCSE level, including English and Maths, increase by 5.7 percentage points. Smacking children could lead to lower GCSE grades, study suggest

https://theconversation.com/corporal-punishment-of-children-linked-to-lower-school-grades-50497 this study showed that "We found that children who reported experiencing corporal punishment at age eight had on average significantly lower maths scores at age 12 in India, Peru and Vietnam. The size of the negative effect was large."

https://www.gse.harvard.edu/ideas/usable-knowledge/21/04/effect-spanking-brain research shows that spanking alters children’s brain response in ways similar to severe maltreatment and increases perception of threats.