I have heard of a few instances where people have adopted a Granny or Grandad for their children. I am not sure - but I think there is an organisation that brings people together for this reason ?
There are lots of lonely older people out there. Some have grandchildren living abroad or have none of their own at all. Its a lovely idea - BUT - you do have to be very careful - apart from suspect people there may be some who like the idea but lose interest very quickly ! - That would be awful for a child if they became 'attached'
Estranged Son and Future Granddaughter
To think that London, or anywhere else for that matter, does not belong to any one demographic