Sir Elton John kisses little Lev in 2009
The singer met Lev Ageyev, six, in 2009 at an orphanage and declared at the time: "I would love to adopt him... he has stolen my heart."
He could not become his parent due to his age - he is 67 - and because gay couples were banned from adopting in Ukraine.
But Sir Elton, who has two sons, said: "I won't give up on him, ever."
At the weekend, Ukrainian socialite Olena Franchuk, a close friend of the star, organised a 460-mile bus dash to get Lev out of Mariupol.
Pro-Russian fighters sit ontop of a tank in Starobesheve
It is thought Sir Elton John and partner David Furnish, 51, were involved in the operation to bring Lev, brother Artyom, seven, and grandmother Yulia Ageyeva, 61, to Kiev.
Yulia said: "People say Russian tanks will attack soon. I thank God for whoever helped us. We've been told we will be moved to a flat and there's a school not far away."
The singer's spokesman declined to comment.
However, Sir Elton John visited Ukraine with his AIDS charity foundation in 2009 and two years previous the singer gave a free concert on the main square in Kiev to raise awareness of HIV and AIDS.
His AIDS Foundation collaborates with the Ukrainian Anti-AIDS Foundation set up by Franchuk, daughter of former President Leonid Kuchma.