London for 3 and 4 year old girls

[Pennies]

We're going to London tomorrow for the day and was wondering where we could go that isn't too crowded and hideous at half term.

I suspect I'm asking the impossible here!

Get wherever you are going as early as you can! People with kids tend to get out later so anywhere at 10am is pretty much ok (I think, I try but tend not to get out as early as that) but by 11.30/12 everywhere is a nightmare.