The essential resource for children to become literate is a culture* rich in reading and writing. Children reared in such a culture will naturally grow to become lifelong readers and writers. Those who grow up in a culture devoid of reading and writing may be taught to read and write on demand, yet are not likely to fully master literacy as independent readers, writers and learners.
Growing up in a culture of literacy, most often referred to as a culture of reading, means children get time to learn about age appropriate books, about people who write well, and about adults who read for work and for pleasure. These lucky kids also are provided with generously long periods of time during which personally delightful books can be discovered and fully enjoyed. Further, and early, they also are given abundant opportunities to create and deliver personal messages to those they most care about.
As with all human learning, children who are new to literacy need a person or group of people who show them how they value and use reading and writing. And children must be shown that reading and writing allow them to engage with those they care about across time and space. Without such demonstrations of value and skill, it is exceedingly difficult for children to become lifelong learners.
Just about any child can learn to read and to write in some basic way, but to become fully active and fulfilled readers and writers takes years of immersion in a rich culture that constantly displays the fulfilling centrality of literacy in their lives. It's very similar to learning a new language by immersion in that language and in the culture of that language.
Additionally, we must keep literacy learning enjoyable because the primary mode for children learning to love pretty much anything is through play. For literacy, that looks like relaxed, playful discovery of the magic of books and books' messages, first with the help of someone reading to them and then by reading on their own.
Given the prominence of picture books for novices, a natural path toward literacy includes children creating artwork to share with someone important to them. Eventually, children will discover the powerful combination of art and text for reaching larger and larger audiences.
I read every day about things to do with and for children and others new to reading to make their reading better. Yes, some more structured lessons are critical for children to provide the help needed for each of them to develop the nuts and bolts for what print, books, writing and reading actually are and what personal needs they meet for the children. However, in the absence of immersion in a culture of reading, instructional lessons alone are likely to arrest children as kids who can read and write at some fundamental level, yet who won't.
*For a comprehensive description and support citations for a culture of Reading Culture, https://www.slideshare.net/ThroughtheMagicDoor/growing-a-reading-culture-1647123