Thompson was born Flora Jane Timms in Juniper Hill in northeast Oxfordshire, the eldest child of Albert and Emma Timms, a stonemason and nursemaid respectively. Albert and Emma had twelve children, but only six survived childhood. One of her younger sisters was Betty Timms, best known for her children's book "The Little Grey Men of the Moor". The young Flora's early education was at the parish school in the village of Cottisford where she was described as 'altogether her father's child'.