Twelve-year-old Daniil Karpenko, of the Russian Urals Sverdlovsk region, received a ticket to the party for winning a model aircraft competition but some officials reportedly removed his name from a guest list because of his diabetes, RIA Novosti reported.
The officials apparently decided after the issue turned up in news reports that Daniil could attend the party, the news agency report said.
The boy will be accompanied by his father.
Since the incident went public, the regional prosecutor's office launched an investigation into the case.
Many children in Russia dream of attending the party and having a chance to see Russian President Dmitry Medvedev, who will attend with his wife, the report said.
The Christmas tree to be delivered to the Kremlin on Dec. 17 is about 100 years old and more than 90 feet tall.