Most keyboards have a setting with sound effects or instrument sounds. My keyboard (see post on January 18) happens to have a setting that includes animal sounds and other common everyday sounds. I made 3 X 5 cards with pictures of the animals (can you tell I like to use a lot of visual cues with my children?) and begin by putting one card on the keyboard.
I usually demonstrate where the match to the picture can be found, then ask the child to press the appropriate key. Depending on the child, I normally present 2-5 cards per session. If they have difficulty remembering where the matching key is, I encourage them to find a "keyboard clue". Is it on the C, the red key, the highest key on the keyboard?
Once the child has mastered finding one sound, we move to two, then three and four and attempt to find the sound in the order presented on the cards. Eventually, many of the children I work with enjoy setting up their own order of cards on the keyboard.
For children that have difficulty following the order of cards, I encourage pointing to each card before playing the match on the keyboard.
Many children could probably identify the sounds of different instruments on the keyboard too. I think the key is making sure you can stay on the same setting or voice for each set of cards.
This activity has also been beneficial when working with children with noise sensitivities. One child I worked with had difficulty hearing the cow sound on the keyboard. After playing this game for a while, she was able to hear the sound if I turned the volume down, and eventually she would pick the card on her own and listen to it at full volume!