The bell is significant in Buddhism, as it enhances meditation by focusing the attention in the present moment, and it promotes a feeling of peace and calm. For children, it helps them tune in to what they can hear and develops their listening skills.
Ask the child to listen closely to the vibration of the sound that's made when you ring the bell. Ask them to silently raise their hand when they can no longer hear the sound, then remain silent for a minute afterwards, listening closely to the other sounds they can hear. You can then chat about all the sounds you each noticed.
You can do this just with one child or with a group. You don't have to use an actual bell — you can use anything that creates a sound vibration.