The sailor in white is Nagorny. I think , but am not sure, that the other boy is Kolya Derevenko, Dr. Derevenko's son. I thought sailor nanny Derevenko's oldest boy was somewhat younger and smaller than the boy in photo. It would help to have photos handy of the Derevenko children, all of them.
Also, at this time after revolution and Nicholas' abdication and arrest, and considering Derevenko's status as a sailor , and Vladimir Derevenko's status as a doctor, it seems more plausible that the boy is Kolya. It might have been difficult and awkward for a mere sailor, even a formerly well-placed one like "Dina" ,to have his children playing around the Palace with the ex-Imperial Family.