Are you sure that's Tatiana? It doesn't look too much like her - such a high forehead. I may be wrong of course.
I know what you mean, Georgiy. I think it is Tatiana, though. Here's one of Maria from the same time:

I believe the family was putting on a play.
Both photos come from the documentary
Nikolai i Aleksandra. It has some nice photos of Nicholas and Ella in theatrical costume too, if I'm remembering correctly. I think I got mine from russiandvd.com. (At any rate, there's a thread about it in the film forum).