Do exactly as kmh suggested and just call in without making an appointment. Ring them first and see how they talk to you, then just call in. Gives you a better idea how the centre is run. In Melb, the centres can be accredited, so check and see if they have any accreditation (these are run by independant people who come and evaluate the centre and rely on parental surveys etc). Ask for a menu of what the kids get and how often is changes. Ask also what qualifications the staff hold who will be responsible for your DD. If they are a good centre, they won't mind you asking lots of questions.

Good luck with your search.