I can understand your reticence, and my children are a bit older than yours, but we have struggled to find babysitters and have been forced to use a babysitting agency here in the UK.
We have been very pleased with the service, they have all been very professional and the children have enjoyed having them look after them. :D
We have no grandparents here to help out, my sister is too busy living her own life and it is difficult to get hold of local teenagers.
All the sitters with the agency must have experience either working with children or in nursing and are well qualified. We have tried using teenagers from the village to babysit, but to be honest I would rather have an adult with experience looking after my kids.
When we get to Adelaide we will be making full use of my in-laws babysitting service!!