The modern world is very different then the world hundred and thousands of years ago. Many of the ways we live our lives are very different then in days gone by.
For example, I went on a excursion to the deep regions of Mexico when I was young with the Sierra Club. It was a 5 day walk. The first day we hiked up a very steep hill the entire day. On the top you could see the ocean on one side and the Gulf of California on the other side. It was a strenuous hike and my body was covered with sweat. But there was no place to wash it off and it dried on my body. The next day I notices something very strange. The insects did not come near me. The dried sweat and dust and grim on my body made me somewhat invisible to the insects.
So if your children lived hundreds of years ago, would they have worn underwear, would they have just urinated or excrete waste on the open ground. Customs dictate how we live. Maybe instead of teaching them to use the bathroom, maybe they might learn to just go outside and use the outdoors.