This is the only explanation I can think of to make logic out of a string of odd things that President Trump's administration has done in relation to their dealings with Russia. I believe that the president sent Mr. Kushner to seek private discussions with the Kremlin through the Russian US embassy because he felt that US intelligence agencies were working against him.
He feared US intelligence agencies would leak his private communications with Russia in order to counteract his policies and strategies.
President Trump has said that he believes the Obama administration was 'taping' his phone calls. I think that he thinks US intelligence agencies are still doing that, even within the White House.