When children have trouble vocalizing a vowel sound, the word doesn't come out right. There is no recognition. The child keeps saying sounds but they don't recognize the word they are *almost* saying.

The short O sound is tricky for many.

Here's a great tip to help with that!

It's always good to have a word associated with a letter to jog the memory. For O we use "olive".
A sliced olive looks exactly like that letter O! To make that sound you have to form your mouth into the shape of an O and an olive. Open nice and wide and say Ahhhh.