is it okay for me to be quiet?

As a preschool teacher, it is within your duty/job scope to clean the toys. Understand that there are typically lesser or no children to tc of on Saturdays and hence, washing of toys commonly take place on this day of the week. From what you had shared, ur boss is understanding of your pregnancy by reminding you to do it slowly. You need to be open in your communication with her if you are unhappy about doing the task. Do not expect all women to understand the situation because not everyone goes through the same experience as you. Go speak to your boss objectively if this duty to the children bugs you still.