ز is one of the most useful letters to introduce alongside ر, because the shape is identical and only the dot tells them apart. Pair them on purpose. Write ر and ز side by side and read both aloud so your child hears that one tiny dot is doing all the phonetic work. This is also when the rule 'never connect leftward' is reinforced, because ز inherits it from ر.

ز sits inside زندگی, the word for life. The first time your child writes their own zay, let them know they have just written the opening of one of the most important words in their language.