Can one sing "twinkle, twinkle, little star" or some such, with pitch? Can tell when the notes are wrong if anyone tries to pick it out on a piano in key of C?

• Or other tunes w/ simple chord progressions like "duke of earl", or that (Mozart?) one I keep hearing in my head, other childrens songs or hymns.
• Choose a piece that is very familiar so the learner can tell when it sounds right or not.