Hi,
could this be your Charlotte?
1841 Census
HO107/485/14/26
Town
Joseph Hearne, 45, Post master, yes
Lucy Hearne, 45, yes
Mary Hearne, 15, yes,
William Hearne, 15, yes
? Hearne, 11, yes - i can't read the entry very well. not sure if the name is Sarah or Harriet but it is a female - suspect its actually Harriet.
Charlotte Hearne, 7, yes
Thomas Hearne, 5, yes
I've had a quick look at the 1861 and 1871 censuses. Joseph and Lucy are still living in Westerham but with no Charlotte.
Regards
Paula