The woman had attended the family day of the carnival with her young child but was attacked amid an ‘altercation’ with two groups of men, police said.
Bryonie Gawith was found dead at the scene and her children Denisty Birtle, nine, Oscar Birtle, five, and Aubree Birtle, 22 months, all died later.
It is the latest blow to the BBC after the Huw Edwards child abuse scandal and bullying allegations on Strictly Come Dancing
A 22-year-old man has been arrested on suspicion of murder.