Well correct me if I'm wrong, but at that point the child would be at school & there would be no child care costs... So that's why being on newstart would be less than working... I think that's the whole point... They want you to work!
Where as a working mum of young children will have child care costs & a lot of the time once you factor in child care costs, it doesn't work out that you are THAT much better off working. I guess that's why a lot of low income workers choose to stay at home.