We are a family of four with children of ages 9 and 14 coming up from Edinburgh and would like help to figure out which tube/bus line(s) would be the best to take. Our train will arrive at Kings Cross around 2 pm. Have 4 pieces of luggage with us. I heard about a boat ride that travels on the river Thames. Would anyone recommend taking the boat from Westminster to Greenwich? This way we can save time for other sightseeing spots that have not gotten to yet. Any suggestions will e greatly appreciated!