The safest options is a trailer, however the only ones on the market ATM that meet Australian Safety Standards is the Cruiser/Croozer (sp?) which is sold in bike stores. We have this & it is excellent, they come in a single or twin & will suits the kids up until around 6 years or 7 years of age.
We have the single one, it has a roll cage, reclined seats, safety harness, 2 attachment points to the bike, if you fall off your bike it wont tip, should something happen to the double anchor point it is also weighted to the left so that if it breaks free it will go to the gutter (away from the cars). It also converts into a pram/jogger.
DF is a mechanic at a bicycle store, Im not sure if Im allowed to mention which one but if you have any Q's PM me & I can find out for you or I can pass on a number you can contact him on.
ETA - Just saw you are in Hastings, I can PM you the addy of the bike store if you want to go in & see him