The 'k' phoneme can be spelt with a 'c' or a 'k' at the beginning of a word.
cat and kitten
There are rules that can help us know whether to choose 'c' or 'k'.
If the second letter of the word is 'e' or 'i' then we use 'k'.
If the second letter is 'a', 'o' or 'u' then we use 'c'.
If the second letter of the word is a consonant (a letter that is not a vowel) then we use 'c'.
Some words do begin ce- or ci-, but in these words the 'c' sounds like 's'.