Under the US immigration law, anyone at any time "knowingly has encouraged, induced, assisted, abetted, or aided" others to enter the US illegally may be liable under the law. If parents did the above to help their children enter the US illegally this law also applies. Simply giving money for the children to enter the US will qualify under this law.
We have seen several cases where parents either took their children to the US and left them here without proper visas or provided material support for their children to enter the US illegally. When they later applied for immigrant visa, the US consulate refused their visa applications.
There are ways to deal with this problem if you have competent legal counsel to assist you.