As Rohini lamented the lack of a Mumbai Storytrails ( this is a link to the blog) , I did some checking..
What you do have are the following
Heritage Walk- guess the walk is not a WIP unlike the website
Nature Trail- sounds interesting and even has an authority figure to back it though targetting visitors from overseas
Time out trails - the first one is most "doe "able :-) though out of bounds for our little ones but I am sure at least some of these enterprising operators will be willing to customise
The Bengalis really do it instyle- they had a city treasure hunt in 2008. Calcutta Walks is a company owned by Iftekhar Ehsan and it organises walking tours of Kolkata, taking you through the city's inherent treasures...of course promoted on NDTV- anything Bengali will be right : - )
And another resource on suggested walks across India covering various city/ town trails ranging from Pondicherry to Jaipur . However I am not sure if there is an escort or a guide or a story teller involved in these trails.
Maybe you can add on what is available in your city or refine this info based on your experience?
This link in added courtesy 'd'
Truly the best of the lot in terms of online portrayal, have you tried it 'd'? Again children below 7 not allowed:-((
And if we do not find too many like the London tour which I loved or the other tours that you read of in blogs of those in the UK or the US( choxbox / mom of 2), maybe we have a good business opportunity here.