"The child is eating bread."
Translation:L'enfant mange du pain.
Because there is no "the" in the sentence. In English, if you say "I have bread" it is somehow similar with "I have some bread" and that translates with "du". If you would say "I have the bread" then you should use "le" instead of "du",
If it would had been "The child is eating THE bread." then it would translate in "L'enfant mange le pain".
You write "l'enfant" because "enfant" starts with a vowel / silent h, so the article contracts with the noun.
Anytime there is a noun that starts with a vowel sound the singular article becomes " l' " and contracts regardless of gender. So "le + homme" (the man) becomes "l'homme" or "la + autoroute" (the highway) becomes "l'autoroute"
Another note, is that the contractions in French are not optional like English. You must make these contractions.