A childhood belief about reproduction

When my mom was pregnant with my sister,(I think) my mom took me to this class of some sort at the hospitalto explain to young siblings where the baby would develop. I don't remember much except the dolls, which were cloth and had velcro pouches that held smaller dolls like pregnant women.

Whether I wasn't paying attention, or they just didn't tell much, I don't know, but because of that I thought for a pretty long time that women became pregnant pretty much at random, which is why women all have different numbers, and some don't have any, even if they want them. The fathers were just the women's husbands, which also explained single moms.