Bloomsbury sounds like a good bet to me. Agree with runningmonkey that if the hotel has organised a package they will be well set up (cold you check to see if they have organised this package before?)
Tubes are quicker - when they work. I ran the London Marathon in 2007 and, living in London, had 2 different train routes to choose from. I was fortuante in that I chose not to take Docklands, as there was a derailment, leaving many runners to make their own way to the start (a mile or 2 away. If I had been involved in that, I think I would have given up!
Plenty of small Italian places around Bloomsbury area, though not sure if they will be open on a Sunday. There is a Pizza Express though, on Coptic Street, also another chain of Italian restaurants in Tott Court Road area which I imagine might be. Will try and find out more info if you wish...no longer in London but used to work in Bloomsbury area, hence plenty of eating out..
Agree that it will be easier to be "central" than nearer the start. How old are your DCs? Their age is something to consider if trying to see from multiple view points, found it quite a struggle when MIL, DC1 and I tried to spot DH. DS1 was in a buggy, and we struggled. MIL did spot DH at one point, but I didn't and felt quite sad. The crowds were a problem, hard to navigate buggy through to good view point. On the other hand when I ran in 2007, DH and DCs (then aged 10 and 6) did manage to see me, both at Tower Bridge (12 or 13 miles I think) and at 22 miles. DC2 did find it hard though, was a long boring day.
I have a place for next year as well, but injured at the moment, so wondering if to pull out. Hoping to try a little run this week to see how it goes....good luck to your DH
SOrry, this has ended up so long....