A couple of thoughts and info. It appears David Sim died just over 1 month after the birth of Margaret in 1923. This would leave Margaret snr with 3 children 5 and under. I suspect she could not cope and both Violet and Margaret were unofficially adopted. Violet to the Scott's and possibly Margaret to Robert and Cassie Gate.
Margaret snr was born 8th November 1894 Brampton, Cumberland. Her mmn was Armstrong.
Only known info re Leslie is his birth, marriage and death.
SS