London in 3 days with a 2-yr old

Buy the RS book. Do your homework. Things in London easy to see as many are close together. Kings Cross has a tube stop so you'll have easy access to the London Underground as well.

If your two year old is a Harry Potter fan, don't forget the trolley on platform 9 3/4.
Otherwise, the many excellent parks in London will be a great way to spend your downtime when the little one isn't doing any more churches or museums.

Split up at times. While one of you tends the child at nap time or early bedtime, the other takes in a pub, theater, pub, museum, or pub. You can visit Coram's Fields. I love their sign, "No adults unless accompanied by a child." http://www.coramsfields.org/

I'm sure your 2 yr old isn't a Harry Potter fan. I would suggest breaking up your day....in the morning go to once place you want to see, then walk thru one of the lovely parks....St. James Park, Kensington Gardens/Hyde Park....are all lovely to walk in. Let your child feed the birds, ducks and squirrels. In Hyde Park there is a Peter Pan statue. There is a great toy store Hamleys on Regent Street your child will have fun and let him/her pick up a toy. Go to Whitehall so your child can see the horse quards up close. You could go to the Royal Mews and see the Queen's carriages and horses. Just a few ideas.

How about the London Zoo? Also consider Kew Gardens. Lots of room to run around.

That venerable publication Time Out London is now on-line and has a great section all about what to do with kiddies. It is really chock-a-block with great ideas. Here's the link: http://www.timeout.com/london/kids/

I'd recommend Greenwich as an option - all the maritime and clock stuff is interesting and the area is full of park space, water views, little shops and restaurants, and nice people. The only downside is it is in east London so you have to add travel time. Hamleys Toy Store if you're nearby was a favorite of my son when he was little. You'll be able to see a lot out walking with a stroller - along the Thames and across The London and Millenium bridges, through Westminster (Abbey and Big Ben, Piccadilly, 10 Downing Street) Kensington (palace, Hyde Park, etc.), etc. you can do markets too - Portobello Road, Notting Hill, etc made famous in movies. I think the Tower of London is good if you don't do an organized tour. They have some interior courtyards and green spaces to run around in if your child gets restless and you need to pop out. They have audio guides too. The V & A museum is also cool and full of wacky and interesting things to see - I feel like it was very family appropriate. I would avoid The Eye unless you take turns. It's zero fun if a young person gets scared and starts to cry. Personally, I think it's overrated anyway, but that's just me.

We visited London several times when our children were small. At the age of two, the simplest things can be fun. Our guys loved riding on the upper deck of a double deck bus. I think we could've spent half the day just doing that, especially in the front seat. Harrod's toy department was always a big hit. The staff was very tolerant of the boys "trying out" the toys. The Peter Pan Statue in Kensington Gardens is fun for all ages to visit if the weather allows.

"I'm sure your 2 year old's not a Harry Potter fan"... Yeah, maybe I'm over-shooting the 2 year old, here. Although, my daughter is about 2, and she does enjoy the stories as I read them. Every kid's different. In the off chance that your little one isn't into them now, but may be in the future, get a photo if you happen to be in King's Cross. Might mean a lot later when you can show that he/she was there. Enjoy the parks.

Darren,, your two year old listens to Harry Potter stories,, I am impressed,, most kids that young are still into books about farm yard animals etc,, your little one is very advanced.. Dev,, a two year old needs a good stroller( preferably one they can recline in and nap in) lots of snacks,, and a few trips to the park,, other then that I would do the stuff you want to do in bits.. however, they will enjoy a visit to the Natural History Museum,, giant dinosaur bones,, and some very fun interactive kids sections.. even for a regular 2 year old,, plus its a interesting museum for adults so you won't feel you are missing out either.
Go on their website,, they have a "kids only " section you click on on the top bar,, there are many things for kids,, I was there kidless and all I could think of as I watched the kids all around me was how much my kids would have enjoyed this museum if there were younger.