I think that even with an almost exact date, it can be tricky to work out who children are from pictures.
In the family photo box, we have 2 photos of little girls who were my grandmothers sisters. My grandmother was one of five girls, but the first two died before she was born and the other two died when she was 2 so she doesn't have any idea which sisters they are.
The best idea we can all come up with is that the pictures were of the two sisters who died when she was 2, and they were taken just in case anything happened to them after the first deaths. But who knows?
I think you'll need to go on probabilities rather than exactitudes. Best guesses may not be correct, but certainly better than labelling the picture "unknown" and hiding her away for ever more. She's so sweet and deserves some light every now and again.
Glen