This is the Queen Alexandra Monument, sculpted by Sir Alfred Gilbert to commemorate Alexandra of Denmark, wife of Edward VII. It reflects the popularity she enjoyed in her own right: when she became Princess of Wales in 1863, Queen Victoria was already in mourning and Alexandra attended many functions in her place. Her public role continued throughout her time as Queen (1901-1910) and, after Edward's death, Queen Mother. She established an annual Alexandra Rose Day when fabric roses were sold to support hospitals, and her monument was unveiled on Alexandra Rose Day 1932, seven years after her death.
Alexandra herself is not portrayed in the monument. Instead, Love sits on a throne with Faith and Hope at her sides. (There are also several rather nice lamps incorporated in the design.) Richard Dorment argues that the composition, and the crucifixion-like pose, add both a religious element and a mourning theme. The child figure itself alludes both to Alexandra's charitable work for children and to the young women who would inherit these virtues.
Gilbert is better-known for another London sculpture, 'Eros' in Piccadilly Circus. It is also a memorial piece, commemorating Lord Shaftesbury whose philanthropic campaigns led to improvements in working conditions and the abolition of employing boys as chimney sweeps.