How can parents teach English grammar to their children when they are not good at it?

Learning grammar is a continuous phenomenon with learning a language including English. Just to have lessons of grammar doesn't work. The best way is to learn English by listening, speaking, writing and reading and get clarifications of grammar during this process. 

General learning is easy through watching English news, reading newspapers and story books and to speak as much as one can.

Observation shows that, parents should just exspose their children, as much as possible, to the grammar they want them to use because grammar exist in the subconscious brain. So it cannot actually be taught, for the purpose of utilizing it. Teaching grammar only ressults in learning about grammar, like for a test. For speaking purposes, all a person need do is to surround themselves with the target grammar, and it eventually emerges. Does it sound too simplistic, or are we overcomplicating this naturally occurring process?

It is easier to teach a child a second language, than it is to teach adults. Children learn by watching and listening to others. The use of visual aids is a good way to start teaching a child English. To teach English you need to know the sounds of the letters and how to pronounce the words correctly. It will be difficult for the child to learn the correct way to speak English if the words are not pronounced correctly.

Grammar is the technical part of a language and as the language evolves so does grammar. If I am not aware of it ,I definitely cannot teach my children. I can only help them by doing courses , giving them books to study  and bringing them along with children who are learning too. Interaction along with studying can help parents teach their children grammar. 

I agreed with Mr. Anayat, and it depends on the children age, the young learner/ children doesn't need to push them understanding grammar directly. 

They can start with basic things like simple past and something like that they at least have to know the basics right?!!