Olivia Uffindell died from injuries when a gust of wind blew her buggy in front of a delivery van, her family said.
This map shows the location of the incident - Woburn Court in Croydon, south London.
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A GoFundMe page was set up by the children's uncle to raise £15,000 for their funerals.
Lindsay Hoyle said his "family will never be the same" after the death of his 28-year-old daughter Natalie.
Police say they have traced four drivers who are thought to have hit the woman, and added that a fifth vehicle may also have been involved.