The BM of my boyfriend's 4-year-old sometimes has "clothing optional" pool parties with her adult friends. My boyfriend and I knew about this before, and weren't overly concerned. Today, his 4-year-old son mentioned that she had a 4th of July pool party yesterday, and that the adults didn't wear swimsuits. He told us that he didn't wear one, either. My boyfriend immediately texted his ex, who confirmed it, saying "You know that my pool has always been clothing-optional, since you lived here." We are extremely concerned that she is exposing their 4-year-old son to this lifestyle, and that he is participating in these parties. I'm not sure if we have any legal recourse, but I would love any advice on this matter. This isn't the first time we've had concerns, either... he just recently (2 months ago) got a bed of his own at her house. He had been sleeping in her bed up until then.