Learn Turkish: Biz çocuğa inanıyoruz.

This is consonant mutation in action! The root word is çocuk (child). When we add the dative suffix -a, the word ends up with a vowel right after the k. In Turkish, when k is followed by a vowel suffix, it almost always softens to a ğ (soft g). So, çocuk + a becomes çocuğa.

Why do we add the dative ending -a to çocuk when the English translation is just "the child"?

In Turkish, the verb inanmak (to believe) always requires its object to be in the dative case (the "to/for" direction). Even though we don't say "we believe to the child" in English, that is how the grammar works in Turkish. You can think of it as directing your belief to someone.

Where does the ı in inanıyoruz come from?

The verb root is inan- (believe) and the present continuous suffix is -yor. Because inan- ends in a consonant, we need a helper vowel to connect it to -yor. Following 4-way vowel harmony based on the a in inan, the connecting vowel must be ı. Finally, we add the "we" ending, -uz.

Do we have to include the word biz (we) at the beginning of the sentence?