The earliest memory I have of when that started, was when my parents sister was preggo and doing my hair. She kept rubbing her belly on my back and I recall it being soft/thick. Another moment is when my gym teacher got upset with me and told me to sit next to her to stay out of trouble

 She made me sit very close and  I saw her belly move, it looked very alien. Then I got a boner when she stood up since I could see her huge under belly with the stretch marks. Another tune was in math class and my teacher was around 8 months pregnant so she was somewhat huge and glowing, she would excuse herself to pee alot (I didn't understand that issue at the time)

 In class she would show how to do math problems, but her belly would be showing the whole time, she would brush my arm against it everytime she would grab my hand to show me how to work through a math problem, I-ll never remember the math problem, but I'll always remember how my elbow felt