Is written correspondence with the child enough to preserve a grandparent's future standing claim?

Written correspondence - cards, letters, messages - can help, but it's unlikely to be enough on its own to establish standing if it's the only form of contact a grandparent has maintained; standing generally depends on showing a genuine, meaningful relationship with the child, and correspondence alone, without in-person contact or a deeper practical connection, is a much thinner basis for that than an ongoing relationship involving actual time spent together.

That said, correspondence isn't worthless - where in-person contact has become difficult or been actively limited by a parent, consistent written contact can be meaningful evidence that the grandparent made genuine efforts to maintain the relationship despite obstacles, which can help explain a gap in in-person contact and show ongoing interest in the child's life. It's strongest as supporting evidence alongside some other basis for the relationship, such as an earlier period of closer contact or caregiving, rather than as the sole foundation for an application built from scratch. If correspondence is largely what you have to work with, a family lawyer can help assess honestly whether it's likely to be enough, and what additional efforts might strengthen your position before applying.