For parents and carers of children.
Here is a very useful summary for parents/carers of children.
HSE - A Parent's Guide to Close Contacts
For children returning to childcare or school following an illness - parents can self-certify the form found on this page, called Covid-19 Return to Educational Facility Declaration. There is no need for a GP letter.
Many schools and creches have been asking parents to get a letter from their GP to say that their child is now fit to return to school. This is not necessary and there is an agreed national process where the parent can complete a declaration form which the school/crèche should accept.