No, it's incorrect. 'Haven't had knowledge' is also very awkward. I'd rewrite the sentence as, "I don't know anything about children who are 3" or "I don't have much experience with 3 year old children".

Well, I guess you are thinking in Farsi and you try to translate it into English and find an English structure for it. Instead, I do recommend you try to think in the target language. Try not to translate what you are going to say in the target language in your brain. You will also face the translation gap which is very bad for you when you are going to speak. you can simply say: I didn't have any knowledge about three-year-old kids. I assume that you already have gained some knowledge. That is why I used the past structure. If you still do not any knowledge about those kids. You can use the present tense.