All four language domains (reading, writing, listening, and speaking) are interlinked and you cannot build just one.
 

Reading comprehension and writing only strengthen when we have a deep sea of language understanding upon which to build, i.e. a wide vocabulary and a broad range of world knowledge.
 

Before we become fluent readers (typically age 7-9) we learn language through speaking and listening.
 

After we become fluent readers, we primarily learn language through reading.
 

As parents, your primary role is to model, mirror, encourage, and support.