It is important that your child understand the difference because most of the reading/spelling rules are built around vowels and consonants.
One of the 1st rules of spelling is the use of "c" or "k". The letter C always soften to /s/ when it appears before e,i, or y. When c is not followed by e,i, or y, it makes a /k/ sound.
A closed syllable ends in a consonant, and the vowel is always has the short sound.