How do parents help their bilingual children build not only oral fluency but also writing and reading fluency in both languages?
The way to become fluent in a language, any language, is to use it in meaningful situations. This doesn’t mean that you need to start racking your brains to line up “meaningful” things to say to your children: any interaction with young children is meaningful to them, whether we adults judge it as such or not.
Talking about things is meaningful, but so is going for a walk together, playing and eating together, laughing and telling off, or just doing things together in silence, all of which activates the language(s) that the child is exposed to from the environment.
Giving the child time to think and work things out on its own is important too. You will be raising a little human being in its entirety, not just a user of languages. Parental uses of language are just one part of the overall patrimony we impart to our children.
Reading and writing fluency develops in the same way as other uses of the languages that are relevant to a child, through need and through use.
The difference is that reading and writing, in the schooling sense of these words, does not come naturally and this is why they need to be specifically taught from a specific age.
Nevertheless, you can expose even very young children to printed forms of communication, for example through picture books, which will make them aware that, say, a doggie is called doggie whether it is a live one or drawn on a two-dimensional piece of paper.
Learning that things, colours, shapes, activities, and so on, can be represented in print by means of drawings is a first step to realising that words, or syllables, or sounds, depending on the script that the languages in question use, can also be represented in print through conventional symbols.
Later on, when the child has started schooling, parents can further help develop reading and writing skills. We can choose age-appropriate reading material in topics that interest the child and that the child will therefore want to read about; or we can suggest writing, together with the child or not, a story “book” (which can be one sentence long, complete with pages and pages of drawings by the child) about the clouds that seem to chase one another across the sky, or a report of some exciting experience to the child, like the dragonfly that just flew in through the window or the first time the child helped out with cooking a meal.
Do feel free to contact me privately, if you wish to discuss these matters in greater detail.