My children are ages ten, thirteen, and fifteen and they have all studied English in school since they were three years old. They do not speak in English because they do not try. I discovered iTalki.com a few days ago, and I think that this may be a good way to improve our English. I think I am at the intermediate level with English and I'd also like to improve.
     I must say that the educational standards at my children's school must not be very high, because after all of those years studying English, it does not seem that they have learned much. Yet they have passed every English class so far.
     I know that my grammar isn't the best. I need some help with it. Thanks for correcting it. 

     This is a good website to practice your second language and gain experience and understanding of grammar and the proper mechanics of writing & speaking. Good luck, Sonia. 
~ Dan 

Helping to my children to learn/practice English

Good morning,
just a few days ago, I found this website, italki, and I thought that it would be a very good website to improve our English. I think I have a medium level English and I'd like to get it better.
My children have 10, 13 and 15 years old, and they have being studying English at school since they were 3 years old. They aren't able to have a conversation in English because they had never tried it (it's that I think).
I must say that the level of (sth eg education) at my children school's isn't very good, but all these years learning English, they must have taught  them something, ??{they have approved every year the subject.}?? I didnt understand this part what did you want to say?
I know my grammatical grammer isn't the best very good and I need some help with it. Thanks for correcting me!!

Mark's correction is good -- here are some additional notes:

"Helping my children...." (No personal "a" in English).
"practice" is used in US English for the noun and verb -- "practise" for the verb is used in British English (and other places using British spelling).
"have been studying" ("been" is the past participle, used after "have" to form the perfect.)
aprobar -- "to pass"
"thanks for correcting me"

Helping to my children to learn/practise English (practise is the verb, practice the noun)

Good morning,
just a few days ago, I found this place, italki, and I thought that it might be a very good place to improve our English. I think I have a medium level English and I'd like to get it better.
My children are 10, 13 and 15 years old, and they have being studying English at school since they were 3 years old. They aren't able to have a conversation in English because they have never tried it (it's that I think).
I must say that level at my children school's isn't very good, but all these years learning English, they must have learned something, they have approved every year the subject. (Should this say they have improved?)
I know my grammar isn't the best, I need some help with it. Thanks to correct me!!