https://www.theguardian.com/commentisfree/2018/jun/05/primary-school-girls-boys-sports-day
In football, girls and boys are allowed to play together up until the age of 18 after the Football Association changed the rules in 2015, and girls’ teams can play against boys’ teams in organised leagues up to the age of 12.
As Dr Hilary Jones said, introducing the debate on Good Morning Britain on Tuesday, girls and boys are physically on an even level at primary age so there is no scientific reason to separate them.