I can provide information based on general knowledge.
Yes, some children may have been told by parents or caregivers that it's okay to pee in the ocean or lake while swimming. The idea behind this advice is that large bodies of water, such as oceans and lakes, are vast and contain a significant volume of water, which might dilute the urine and make it less harmful. In contrast, peeing in a small pool might have a more noticeable impact on water quality.
However, from a hygiene and environmental perspective, it's generally recommended not to pee in any body of water where people swim. Urine contains waste products and bacteria that can potentially affect water quality and lead to health hazards. It's more considerate to use restrooms or designated facilities when available to maintain a cleaner and safer swimming environment for everyone.