Hello, any family friendly Harry Potter theme restaurants in London or close to something like that? Any Harry Potter theme afternoon tea places?
No Potter themed attractions of any kind outside the main tour at Leavesden studios. The Potter franchise are very, very, VERY hardcore about controlling the brand and maintaining quality standards.
There are no Harry Potter restaurants as stated above but London Walks has two Harry Potter themed walks
Also you might enjoy visiting Leadenhall Market. There's not an awful lot to see there but it was the inspiration for Diagon Alley (or one of them - Victoria Street in Edinburgh also claims this) and there are a couple of cafes and restaurants there.