Thank you for your response. I feel very bad. My spouse is now on medical exam step. Does it mean my application got approve? I will find a good time to tell her.
No, medical does not mean it's approved. Although it does likely mean you were approved as a sponsor.
Did you submit any forms where you left this information out? You should correct them right away. Just explain in a letter that you are not in touch and thought it was not important as they are adults and citizens (ie not dependents) and you are not in touch.
Now I don't mean to overly scare you. If your children are adults, it's not necessarily material information. Just correct the omission. Better to correct yourself before it is discovered.
You left out some info like whether you are a citizen, when your children immigrated, etc. If they are not adults, though, it may be more sensitive and you should consider seeing a lawyer.
Note, I am NOT a lawyer or immigration specialist. It may be better to see if others have info on this. So don't act too hastily, as this is just one opinion.
But in terms of your spouse, just get it over and tell her. That's actually the easy part.