I've studied the science linguistically but I'd like to put that aside. PLEASE teach your kid the native language. It can go so much deeper than "wondering why", it can create a schism-like pain when you know there's a heritage you have but all access has been cut off. Yes, ALL. If you're fortunate enough to visit the country of your native language but dont teach your kid, they will be miserable, quiet, and alone, and go through difficult phases of hating that heritage because the ladders were cut for them.
And in the United States, this starts young. I've seen teachers tell a Kazakhstani parent that she should tell her kid to speak English INSTEAD. The kid was 2 and a half. A friend's five year old told him "Dad this is America we dont speak Chinese". If you don't teach your kid your native language this country will wrest all pride and heritage from them by force. An occasional visit or two to the home country will not stop the bleeding.
The pain of not speaking the language of my heritage is something I don't wish on anyone. And that language is one of the most spoken in the world, imagine if your native language is rarer. What happens? What happens?