I just read a great comment on a Noteflight score by composer mentor @mcclellan! Often times students when creating their first melodies will use only 1 or 2 different pitches.
Here is what Robin wrote;
"I love what you have so far. It's interesting how you keep the melody in a small range of notes. How many different pitches (each pitch = one note name in the musical alphabet) you used overall? Try counting them (leave out repeated pitches) - and then for your next section, try adding only one more! Even one added pitch can add a lot of excitement to your tune."
Feel free to "steal" this great comment to help your students who may only be using a few different pitches when creating their first melodies.