Well they are young boys out on an adventure>
They could have physically discovered a sense of hardship and camaraderie through their adventures through the bush, etc.
They could have made an intellectual discovery regarding the confronting nature of their actions and also their ignorance (when teddy screams at the train trying to be like his father)
There are heaps of things you could take from that movie but if your looking for specific techniques I recommend you break it down to what was the visual technique (camera angle, colour, any sounds? etc) and then try and think whether you could bring in a literary technique (was it symbolic for anything? did the scene have a metaphoric meaning?) after selecting a specific event.
