Why do your vowels examples ("aaah", "eee", "uhh") sound different then when I make them? Explain.

Tension, mass density and the length of our vocal cords differ so would that be the reason why they sound different? For instance: a child's voice is usually higher pitched than adults because the mass density and length of their vocal cords are typically smaller. This causes an increase in frequency which means an increase in pitch.

Is this correct?