Talk about the trip to the bathroom before you go. Lay out the expectations you have for the group, including that they remain quiet. Any deviation from the norm is often an invitation to speak to other students who may be close by. Have this discussion each time you leave the class for a bathroom break.
Offer incentives to the preschoolers. Young children often respond well to reward systems. For instance, let the class know that each child who is quiet on the trip to the bathroom receives an extra five minutes of free time. A long-term reward may also work with some students, such as the promise of a sticker or pencil at the end of the week for remaining quiet on all bathroom trips. Alternatively, give the preschoolers a certain number of tickets or other tokens they can redeem for prizes after a certain amount of time. If a child is not quiet and requires a warning, he loses a ticket or tokens.
Establish a visible warning system for the preschoolers. Young children often quickly forget instructions unless they are reminded. Some visible warnings include holding your finger to your lips, counting down from three on your fingers, pinching your lips together or shaking your head. Remind the children of what your chosen cue means each time you leave the classroom.
Stand outside the bathroom door while the preschoolers are inside. Your presence will serve as a reminder of your expectations. If you cannot be near both the boys and girls bathrooms, team up with another teacher so you each can take a door.
Issue punishments to the children who do not obey the quiet rule on the way to or from the bathroom. For instance, those children who are not quiet may need to sit quietly at their desk for five minutes while the other children begin free time.