Well, there isn’t any.
If you’re teaching a kid over the age of (whatever), they already understand the concepts of cause and effect, conditionality, future, past, and so on.
Grammar is just the way language expresses the relationships between things and actions. So the things or actions in these cases just happen to be occurring in the future, or might occur if something else happens.
Don’t think of it as grammar; think of it as meaning.