This appears to be Thomas and Mother in 1851 Census;
St George Hanover Square
Martha Brown, 41, Wife, Mar, Chandlers Shop Keeper, born Lambeth, Surrey
Thomas Brown, 11, Son, born Pimlico
Emily Brown, 1, Daug, born Pimlico
BROWN, EMILY, Mothers mn DAVIES
GRO Reference: 1849 J Quarter in SAINT GEORGE HANOVER SQUARE Volume 01 Page 17
I cant find them in 1861 Census or Thomas B Brown in 1861 either (he should be married with a Daug Elizabeth age 1)