"The child has a gray shirt."
Translation:L'enfant a une chemise grise.
Gris, as an adjective meaning 'grey', must agree with the gender and number of the noun it describes. Chemise is a feminine noun in the singular, so we must use grise.
Mon chien est gris - My dog is grey (chien is masculine and singular, so we use gris)
Mes chiens sont gris - My dogs are grey (chiens is masculine and plural; the plural form of gris is fortunately the same as the singular, because it already ends in an S)
L'enfant a deux chemises grises - The child has two grey shirts (chemise is feminine, as already established, but now there are two shirts, so we use grises which is the feminine plural form)
The way I see it it's like the equivalent of using "a" vs "an" "an" for words beginning with a vowel (AN apple, AN orange) and "a" for words beginning with a consonant (A carrot, A child). So, in French when a word starts with a vowel we remove the 'e' from "le" and the 'a' from "la"
Vowels; l'enfant, l'araignée l'orange, l'eau (also, because the 'h' isn't really pronounced;) l'homme. Consonants; le chat, le chien, la fraise, la beurre, etc