This is a simple, but important tip that will help all young musicians: learn your ABC's backwards!
The musical alphabet is only 7 letters: A B C D E F G. As piano students learn to play the keys on the piano, it is often easy for them to figure out the letter names of the notes as they ascend. Its easy because the music alphabet goes in order, but the tricky part is figuring the letter names as the notes descend. Thinking about the music alphabet in reverse order, quickly, is often very challenging.
In order to help your young musician achieve success in this area, help them practice saying the letters backwards. Start at G and work backwards to A, then ask what comes before the A....its G! Then start at a different letter and work down, and so on and so forth. This will help with the quick decision-making that they have to do when playing.