Rhythm
A fun way to develop rhythm is to clap a pattern, then encourage your child to repeat it! A video example of this game is here. Have your child repeat this game. If they want, they can think of the pattern and you can clap it back.
Pitch/Notes
Recognizing notes and pitch are important in developing musicians. Sing or play high and low notes. Have your kids reach for the sky during high notes, and crouch down to the ground for low notes. An example of this game can be found in this video.
Another way for kids to engage with notes is to sing songs to them or with them. They will recognize tunes and become better at remembering notes and melodies. Call and response songs are a good way to begin this process. A call and response song is one where one person sings a tune, then the other person repeats both the lyrics and the pitches. An example of this is the song, "My Bouncy Ball."
Expression
Music is used to express emotions. Sometimes music is meant to make the listeners feel those emotions or communicate a message to the audience. This Sesame Street video does a great job explaining how music can express multiple emotions. After watching talk with your child about a song they know or like. Have a conversation about the way the music feels to them and why they feel that way (Ex: Is the music slow or fast? Are the notes smooth and connected or fast and bouncy?). Try listening to a song they haven't heard before, such as one on the list of kid-friendly songs, and ask how they feel during the song.
Instruments
An instrument is a device used to produce music. From a singing voice to household objects, encourage your child to see musical instruments in the world around them. Sesame Street has a song about finding instruments and making musical sounds.
There are also instruments specifically for music making. Talk about musical instruments to your kid. Play a song they like and point out distinctive instrument sounds such as piano notes or guitar. A good introduction to some more classical instruments is this Instruments of the Orchestra song.