with two little ones i definately recommend the tumbling waters caravan park if you can get in as its very popular, and very family friendly with an array of activities at the park including a pool. check their website, im pretty sure you can book online too. Second option would be the berry springs caravan park called 'the lakes' its ok, has a water slide which is nothing special and the lakes are mainly used by water ski'ers, not really for swimming, another billabong is used for leisurly paddleboating or cannoeing, probably not that suitable if you have little ones, if you have a choice between the two then i definately recommend the tumbling waters caravan park. websites are follows
http://www.tumblingwatersholidaypark.com.au/
http://www.lakesresortcaravanpark.com.au/