A father has described how his eight-year-old daughter was "pelted with coins" during clashes between West Ham and Chelsea fans.
Violence broke out during the EFL Cup match at the former Olympic Stadium, which resulted in seven arrests being made by police.
During the unrest in the stands plastic bottles, seats and coins were hurled among the crowd. The Football Association has now opened an investigation into the matter.
The the girl's father told the BBC: "(She's) been going since she's two. She's never experienced violence like this before or the aggression that we've had to suffer.
"We've never been hit by coins before - to be hit by seven of them in one evening, that's why we've kept them. We want to take this matter further."
Skirmishes broke out towards the end of the Hammers' impressive 2-1 fourth-round win as police and stewards battled to maintain segregation behind the goal being defended by West Ham.
This derby was billed as the biggest footballing test for the London Stadium so far, on a night when basketball and track cycling competitions were also taking place on the former Olympic Park.
Met Police said seven men were arrested for public order offences.
They were taken to various police stations in London.
In addition, 30 people were issued with directions to disperse under antisocial behaviour legislation prior to the match.
Commander BJ Harrington, who was leading the police operation, said: "There were unacceptable incidents inside and outside the stadium, before, during and after the game.
"We welcome the condemnation from partners and have already started a post match investigation.
"We have already made seven arrests and will work tirelessly to identify people involved and bring them to justice."
Anyone with information or witnesses to the disorder is asked to call the police non-emergency line on 101.