Could you advise if it is recommended for children under 18 months to sleep on a stretcher bed instead of a cot in a long day care centre? Could you provide a link to information to support this? Thanks

Red Nose,  recommends that the safest place for baby to sleep is in their own safe sleep space (eg cot) that meets Mandatory Australian Standards on a firm, clean well fitting & flat mattress.
https://rednose.org.au/article/what-steps-can-i-take-to-sleep-my-baby-safely

General information for moving from a cot to a bed includes the following
Red Nose
For safety reasons, when a young child is observed attempting to climb out of the cot and looking like they might succeed, it is time to move them out of the cot.
This usually occurs when the child is between 2 and 3.5 years of age but could be as early as 18months.
https://rednose.org.au/resources/education  see  Cot to Bed Safety brochure 

Other specific information for Child Care includes:

ACECQA information
https://www.acecqa.gov.au/resources/supporting-materials/infosheet/safe-sleep-and-rest-practices 
Babies and toddlers  
Babies or young children should not be moved out of a cot into a bed too early; they should also not be kept in a cot for too long. When a young child is observed attempting to climb out of a cot, and looking like they might succeed, it is time to move them out of a cot. This usually occurs when a toddler is between 2 and 3 ½ years of age, but could be as early as 18 months  

It is difficult to place an exact age on when baby should (or should not) move from a cot, & it is important for risk assessment to be made when child needs to be moved from cot.

Risk assessment should highlight issues around baby’s development stage &/or readiness for moving from cot to bed.  
If child is attempting to climb from a cot & looks like being successful, then child needs to be moved to floor mattress (or similar) to reduce the risk of falling from cot, regardless of age.  

​**If a child younger than 18mths is being slept on a mattress/floor bed, consideration needs to be given as to where this child is slept, what risks are there in the child’s environment (what do they have access to now they are no longer in a cot) & what supervision is being provided. 

Supervision of sleeping children is an important regulatory requirement. If a baby is placed on a floor mat/mattress, then supervision & planning is important in relation to environment when a baby is not within a cot. ie what does baby have access to now (in the Centre or home) that they would not have access to if they were in a cot.
https://rednose.org.au/article/making-your-home-safe-before-moving-a-child-from-a-cot-to-a-bed
https://rednose.org.au/article/transitioning-from-a-cot-to-bed

NSW Dept Education has some information about adequate supervision of children that might help guide your Policy.
Sleep and rest for children – Policy guidelines for early childhood education and care services