One of the ways how to achieve this is to use different music scales.
The most common scales which are used in the western music are major, minor (with 3 variants: natural, harmonic and melodic) and pentatonic scale. A simple hint - pentatonic scale are black keys on the keyboard; these are simple to use by children themselves.
However, these are not the only possible scales. Different cultures have developed different scales. There is a nice list of them here.
Furthermore, the scale depends on the sound spectrum of the instruments - our scales are suitable for string and wind instruments. But we will discuss this in more details another time (sign up here).
Anyway, think about it and use it in your teaching!