Is your kid in Talent Plus Playgroup? My boy was with Talent Plus Playgroup at Anchorvale and I had the same issue.
For my case, the teachers did not mention from the start that the caretakers have to be on standby to change diapers when my boy poos if not i would not have enrolled him. Instead I received called from the school twice every week asking the caretaker to go down to change his diapers. I had to go down to speak with the teacher many times and each time it is a different reason (eg. some parents prefer it that way, my boy is not cooperative, my boy appeared to be in distress etc). I told her my helper would take 20-25mins to reach the school but they will rather wait. Whenever my helper goes to change the diaper, the teaching assistant gives another set of excuses (eg. they do not provide diaper changing service, too many kids no time to change) and even instructed my helper to just wait at the backdoor everyday, she will call her to change when needed.
I even messaged the centre manager to confirm if the school does not change diapers but i got a reply that the teachers will change if the parents are uncontactable. Sadly, that was not the case as there was once I was in a meeting and received many missed calls from the school, panicked and thought my boy might have hurt himself in school. Called my helper who said that the calls were for the same issue - my boy soiled his diapers. The teaching assistant even questioned her why she called 5 times but noone picked up. Did they change the diapers even though i was uncontactable? Unfortunately no.
I spoke to the other caregivers who also said the same - they were all asked to go down to change diapers, no exceptions. Therefore, I pulled my son out as I can't control when he will soil his diapers and it has caused me much inconvenience. (I even got my helper to practice how the teacher said the diaper changing process will be so that my boy can get used their method) For my case, I feel that the teachers were not honest about the diaper changing issue - if they do not change diapers, just say so instead of misleading parents and conveniently blaming my son for being uncooperative. Asking parents to pack a spare diaper in the bag when the caregiver has to go down anyway makes no sense to me as well.
I have been checking and asking around the other playgroups and it seems like the teachers will help to change diapers if the child soils their diapers during class.