According to Onestopenglish, a site for English language teaching materials published by Macmillan English Campus, it is difficult, if not impossible, to teach grammar formally to children under the age of 9. Your child or student will have great difficulty if she is below that age, because she will not have passed through the so-called preoperational stage. This means that concepts such as past continuous are just too difficult for her to understand. Her learning will be by clear contexts such as stories and cartoons.
When you are teaching grammar, it is easy to confuse your students. There are several reasons for this. One reason is that some parts of grammar can have more than one meaning; for example, a statement in the present continuous such as "John is playing with his friends" can imply that the action is taking place right now, at the present time; or these these days, that is past, present and future; or even in the future. So be aware of such potential difficulties, and shape your topics so that such issues are taught with clarity.
Understanding, say, what a noun is can be easily understood by children or students above a certain age. However, extend your topics into more-complicated areas, for example, to noun clauses. Use the words of songs, and ask your students to recognize and extract them from the lyrics. Sometimes students have difficulty understanding the difference between particular aspects of grammar, for example, active and passive voices. One way of dealing with this and similarly confusing aspects of grammar is to create an activity where students are given sentences in one of the voices and asked to change them to the other. One more participatory activity is to use the board as the medium for writing, split the class into two teams and have each team member in turn change a sentence on the board. Speed and accuracy are rewarded to determine the winning team.
Learning to understand grammatical correctness is a cognitive skill. For this reason, students can gain understanding by being engaged in cognitive activities associated with particular aspects of grammar. So if you want your students to better understand, for example, simple past and past progressive, put a lot of separate words on the board, on a handout sheet or cut up into single words. You can list them in categories -- for example, nouns, pronouns, adjectives -- and get your students to format sentences appropriate to your instructions.