HELP:Precruise days (# ?) in London + 13 yr old Birthday

[Emma1]

We are doing a cruise out of Dover to the Baltics and would like to spend a few days in London. There are 5 of us and our children are 10,12,14. Would like your thoughts on what I envision doing. Cruise leaves out of Dover on 7/6. Thought of arriving in London on 7/2 for 3 nights. Leaving on 7/5 morning for Dover to see the Castle plus a stop in Canterbury (thought of hiring a car service for these two tours). Spending 7/5 in Dover to be at cruise early on 7/6.

 

-Is 3 days in London - I assumed 2 days would be too rushed?

-My 12 year old daughter will have her 13th birthday on 7/3 - what would be a good thing to do - a fun place to go to dinner where we can get a cake and for the waiters to sing happy birthday?

-Is it better to get a taxi or take National Express straight to Dover and then do local cabs to Dover castle and Canterbury?

[Twickenham]

-3 days in London is acceptable - woefully inadequate, but acceptable :)

-With 5 people, I would seriously consider renting a car for the whole London-Canterbury-Dover trip. If you're talking taking a cab from Dover to Canterbury this would cost a fortune, and trains aren't really cost-effective with 5 people. If you do rent, don't go back to LHR; either rent from an agency in town, or if you fear driving in Central London, go out to either Croydon or even LGW, which are closer to Kent. I believe there are rental agencies (National?) at the port in Dover where you can drop off the car on the day of the cruise.