NO NO NO NO!! You need to change your policy ASAP. I have ran into this problem before too. Parents don't have a clue what goes on at daycare. We do not have time to potty train like they do at home and I certainly don't have time to clean up floors and kids every time they have an accident just because the parents think they are trained. Also I have carpet and I do not appreciate kids peeing on the carpet. Here is what my portion on potty training states in my contract:

Potty Training:
If you are toilet training your child and would like me to continue with it during the day I would ask that you send pull-ups to use in my home. Once the child has consistently had a dry pull-up and tells me when they need to use the washroom for 2 weeks we can try to transition to underwear. Please do not send your child in underwear until I have agreed to it (there are way more distractions at daycare than at home and it usually takes longer for them at daycare to become fully trained). I also do not have time to place your child on the potty every hour and wait, they need to be able to tell me when they need to go.