It's very nice that your friends are taking time off work to spend time with you.

They may have planned a very busy sightseeing schedule for you already.

But OTOH, they may not.

It's best to do some research yourself so that you'll have some idea of what you want to see/do; and consult with your friends.

If I were hosting someone at my house - I'd be annoyed if they had no idea of what they want to see/do and rely completely on ME to be their tour guide.

If your friends in London live outside of the city (which, as I said before is not unusual, given how expensive London is), it's not uncommon to have a 30 or 45 minute commute INTO the city.

I don't have children myself, but I assume your kids, esp the 5-yr-old and 1-yr-old, will get tired during the day.

Do your friends live close enough so that you can all go back to their place for your kids to nap?

If your kids can stand an all-day excursion in the city, can you and your spouse possibly carry all the stuff you need (diapers, toys, formula) with you all day walking around?

Of course, if your friends actually live IN the city, then you don't need to worry about it.

They are good enough friends to stay w/ but you don't know where they live? Have you ever sent them letters or cards?? If so you would know what towns they live in . . . . . .