There are government guidelines for schools about health protection and managing specific infectious diseases at GOV.UK. These say when children should be kept off school and when they shouldn't.
If you do keep your child at home, it's important to contact the school on each day of your child's absence.
If your child is well enough to go to school but has an infection that could be passed on, such as a cold sore or head lice, please let their teacher know.
The following link is very useful in helping to decide whether your child is well enough to attend school, and school would always contact parents/carers during the school day if we felt that your child needed to be collected,
Is my child too ill for school? - NHS