Chatherine Wynter, 19, also known as Katie, was staying at the house on Boxing Day night while the children’s mother was away.
Miss Wynter’s mother found her body when she called at the address in Borehamwood, Hertfordshire, at 8am the next day, Detective Superintendent Michael Hanlon said.
He said the children, aged three and four, were still in the house but they had not been injured.
Specially-trained officers are interviewing them and do not yet know how much they saw or heard of what happened to their aunt, who regularly babysat as a favour to her sister.
The interviewing process is expected to take some time because of their young age.