There are various websites that can provide you with information on police checks in Australia but ensure that your first point of reference is the official AFP website. Several professions require that police checks are completed before anyone can be taken up for employment so you might as well want to check whether you would be required to do so for any new job that you may be looking forward to applying.
If you are looking forward to working with kids, especially smaller ones then it would be necessary for you to be cleared by the police in order to be able to be employed and your employer would probably ask you to go for a police check for which you will have to scour through the internet to find relevant information that may be useful to your purposes.
For anyone above the age of 16 who has been a resident of Australia for several years, a police check Australia is possible for a small fee and you would normally be asked to complete an application form and submit it and this can be done through a range of websites that you can find through Google.
Be sure to apply for a police check well in time instead of waiting till last moment as you may not be able to get it quickly and this is something that would entirely depend upon how you proceed towards getting one.