Go to a pie and mash shop,,, the natural history museum ,,, I quite liked the food court area in harrods,,perhaps not the place for your kids though....oh go and see the bomber command memorial,,, which is near Wellingtons statue..
Few years ago I went to planetarium ,,,that's good,, and cos its next to madam tusards you get in cheap with a double ticket,,,mind you I thought tusards was shite,,, London eye is good,,,