Abby Wood London - Travel Into London

DanR

Hi There, we are staying at Abby Wood for five nights over Easter - we plan on traveling into London to see the sites for four days (during the week). 

I was wondering if anybody  can suggest any cheap travel options into the city?  I know the site is near a tube station and there is a river taxi also - was wondering what ticket options would offer the best value?  There will be 2 adults and 2 children
(5 & 8yr olds).  we would need travel in and likely tube usage during the day to help get around.

Thanks in advance.

Dan