what are safe sleep requirements for older children in a kindergarten room i.e. to children need to have a fitted sheet as a barrier between the child and a portable bed ?

Red Nose has no specific information in relation to your question.
Using fitted sheets or other sleep environment recommendations (general in nature) can be found in information provided by ACECQA.
https://www.acecqa.gov.au/resources/supporting-materials/infosheet/safe-sleep-and-rest-practices

Sleep & Rest Policy guidelines for all children.
In some sections ACECQA will refer to infants, in other reference is to children in general.
P6 - Procedures
https://www.acecqa.gov.au/sites/default/files/2024-08/PolicyGuidelines_SleepRestForChildren_August2024.pdf
Also P4, Sleep environment has the following:
“How does your service ensure the physical environment caters for non-resting children? (Consider separate resting spaces or quiet activities after a short rest.) How will quality practice be reflected in your policy?”

Red Nose is unaware of any requirement that children need to have a fitted sheet on a bed, however they are generally easier to use than a standard sheet. Ensure child’s head & face remains uncovered.

What State are you from?
Check any specific information from your Local State Regulators.