I think may be Gunjan herself in unaware that she has a kid with Samrat....it may be possible that after giving birth her family especially her Bauji and Bui who are very conservative told her that her kid was still born and had hidden the kid from her....and so she was working in the orphanage amonst the kids only.....
that's why even mayank is unaware of sajan's kid....he may be knowing that the kid had died....but not that its still alive.....
otherwise I see no reason why such a small kid is not with his mother and mayank hiding such a truth from samrat. Also Mayank told Samrat during their initial conversations that Gunjan suffered a lot because of him.....and that's also the reason why Gunjan doesn't want to back to Samrat.
What you all say?