I think they have to be school age but there is a soccer program for preschoolers. It's called Soccer time kids, They run one in Croydon.
According to the FAQ "children must turn 5 in the calendar year to participate" so that's us - DS1 will be 5 in May

We looked into the local soccer programs, but they're so bally expensive. The ones around here are mostly about $18 per week (plus uniforms) for a 30-45 minutes session -- compared to Auskick which is about $30-70 for the whole season of 60-90 minute sessions.

We're looking forward to it, and I'm trying to get in the spirit of AFL ... ! I should probably learn the rules, etc ... not sure how I've managed to get through 33 years in Melbourne without having done so yet (though I did play in the grid game one AFL final! And I've gone to the footy 3 times! woot!)