Call the museum ahead of time to find out who is the featured artist.
Most museums also have an ongoing permanent collection.
Sometimes it is possible, during the weekdays to join a school tour lead by the educational department. Find out if there are special materials available for your child to receive when they arrive at the museum. Call the educational department of the museum and ask to speak to the educational curator. Ask them if there are materials available for you to review or receive that will explain art through a child's perceptive. Purchase a few postcards ahead of time or buy a catalog of the show.