Hi, What would happen in your setting if a parent came in to tell you this?
Can you ask for a copy of the policy and procedures? With that you'll be able to read what's expected of you in these situations eg. which records need to be filled in and what information needs to be collected from the parent.
https://www.nhs.uk/conditions/diarrhoea-and-vomiting/
It is important to know these details as a child can become unwell quickly.
You may be expected to ask the parent if there are any possible reasons for the child's loose stool or diarrhoea eg. if anything had changed in their child's diet, if they've been unwell, vomitted, visited the local GP surgery, taking newly prescribed medication, had any vaccinations.
Would you need to tell a colleague or a more senior member of the management team?
Page 72 & 76 of this level 3 handbook looks at what to do when a child is ill
Hth xx