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the preteen boys in his class discuss a lot of topics that are very sexual in nature during breaks etc. This has mostly been beyond DS's comprehension so far, but we are expecting that he will begin to catch on to it soon. We don't know yet how to deal with this.
In this old thread and others, several parents mentioned finding age-appropriate books and helping their children learn about sexual matters, bodily changes, and vocabulary (scientific and slang) at home before they learn it at school.