Alan and Laura Shatto, who adopted the Maxim Kuzmin, 3, and Kirill Kuzmin, 2, face no charges over the death of Maxim and still have custody of Kirill, RIA Novosti reported Saturday.
Maxim, whose bruised body was found outside the couple's house, had a history of hurting himself.
Texas authorities have refused to return Kirill to Russia.
Konstantin Dolgov, the human rights envoy for the Russian foreign ministry, said Kirill's case will be discussed this month during talks on adoption in Washington. Russia has banned U.S. adoptions in response to a U.S. law creating economic sanctions for officials involved in human rights abuses.
Under the old agreement, Russia had the right to cancel adoptions and ask for the return of Russian children. The new law, which does not take full effect until the end of the year, ends that.
There have been documented cases of abuse and neglect of Russian adopted in the United States, although experts say they are few compared to the number of adoptions.
Officials in Texas said in February a Fort Worth adoption agency that placed Maxim Kruzmin for adoption was under investigation following his death.