...walking along Southbank is one of the most beautiful ways to see various sites of London.
Starting from the London Eye, overlooking the Thames, Houses Parliament and Big Ben.
The Royal Festival Hall in particular, is an excellent meeting spot and place to chill... sometimes you get art or music for free in the foyer :) and there's a cafe and bar for refreshments!
There are plenty of tourist-friendly/child-friendly restaurants around here, big chains such as: Waggamama, Strada, Giraffe, also a pretty big "eat" (with great sandwiches, juices etc,.) a bookshop and music shop too... plus a regular book market outside the BFI, in the summer various free events outside, well worth checking out this area and just walking, walking, walking...
Is this your business?