As a Primary School Principal I send this out every year.
You have two choices:
School cover only
24 hour cover
Children are covered in school by the school's own insurance but negligence has to be proven before it pays out. For example, if your child falls in the yard and medical fees are incurred you'll have to pay them. If the school is found liable then they'd have to pay but that could take time/effort to prove.
If you take out the extra cover that's offered the policy will pay out immediately for medical expenses etc. as listed on the form you receive. You don't have to go through the process of proving that the school was negligent.
24 hour cover does as it says ... it covers school hours and when the child is at home etc. So if your child, for example falls at home and incurs doctor bills etc ... you send them off to the insurance company ... they reimburse you.
It a great idea and well worth having it for the reasonable cost involved.
Normally the policy runs from the start of the school year until the end of August. Why is it being offered to you now half way through the school year?