It happened again last night

I must make more noise than I think when I am going to bed because a lot of times one of the boys will get up to go to the bathroom. I'll just be getting snuggled in and I will hear the all too familiar "mmmmooooommm, I neeeeeeeeeeed YOU." At what age do boys realize that if they sit down to pee and they don't point that thing down, they ARE going to pee all down the back of their pants? Haven't they discovered that where they aim - the pee will follow? One day 2 summers ago I stripped them down to their underwear outside and then went in to run their bath water. While inside, the phone rings and it is the elderly neighbor lady laughing her head off - calling to tell me that all three of the boys were outside running around naked - peeing on each other. They seemed to have pretty good aim then. What's happened in the meantime?