I think Leviticus was written because the Egyptians must have practiced all these things, so God attempted to set-up a new system for Israelites. I think the bathing & all that was maybe because they were not known for being clean. Always throwing dirt on themselves, or ashes, tearing their clothes and such. Maybe the Israelites were not the cleanest folks in the world. If they had to be told all this stuff, most likely they were practicing these things.
We know we are not supposed to have sex with family members, no matter how removed they are...as far as the semen stuff, could be if one had an emission without sex, that's an indication, something isn't right...I think his concern was transmitting illnesses, being they didn't have modern medicine like today, the only way was to give it time to clear up. Could be the Israelites were a horny bunch (no doubt riding bare back on camels & horses, enough to make anyone excited.LOL)....didn't care whether the female was on her menstral cycle, or just gave birth, the men wanted sex when & where they wanted. Remember women were only property & baby machines.
I don't think this is appropriate for children, but the witnesses want to keep their kids close, so they don't care what they hear, as long as it's from the hall. But when you come to think of it, most of the kids aren't paying attention anyway...it's mid week, so them little ones are sleeping...just like us adults.