This is a prompt that I did with my writing group recently. Take a main character from a very young age group - say, 3 to 5 years old. Put the character into a situation that might be easily navigated by an older character, but is perhaps more difficult to grasp from the perspective of a very young child. Write for 15 minutes about what the child sees, hears, thinks, and does in the situation. You can select a situation from the list below, or make up your own.
A child goes to the library, where he must be very quiet.
A child goes to a first doctor's appointment.
A child goes to the grocery store for the first time.
A child goes to a theme park for the first time.
A child goes to a wedding.
A child goes to an all-you-can-eat buffet.