Latest government guidance for Covid information can be found below.
Reducing the spread of respiratory infections, including COVID-19, in the workplace
Within that link is the following one which gives specific guidance as to what to do if you have symptoms and HAVE taken a test and if you have symptoms but NOT taken a test (You do not need to take a test.
People with symptoms of a respiratory infection including COVID-19
Children and young people aged 18 years and under who have a positive test result
It is not recommended that children and young people are tested for COVID-19 unless directed to by a health professional.
If a child or young person has a positive COVID-19 test result they should try to stay at home and avoid contact with other people for 3 days after the day they took the test, if they can. After 3 days, if they feel well and do not have a high temperature, the risk of passing the infection on to others is much lower. This is because children and young people tend to be infectious to other people for less time than adults.
Children and young people who usually go to school, college or childcare and who live with someone who has a positive COVID-19 test result should continue to attend as normal.