Hi ℨ𝔞𝔯𝔞. I agree with Ash73 that you should do chemistry -- not only does it form a foundation for a bunch of different degrees, but it's also a requirement for some undergraduate medical courses like Monash and Curtin.
I'd also recommend biology. I don't believe it's a hard requirement, but I know that Monash recommends it for med entry. If you haven't done it you can still apply but it'll be recommended you complete an online VCE Biology bridging course between high school and uni.
For the rest of your subjects I'd recommend simply doing what you enjoy most. It's very competitive to get into medicine and doing subjects that you enjoy studying will help.
Finally, being a pediatrician requires extensive study. Even after graduating medicine you'll have some pretty tricky exams to do for a few years. If it's what you want, then I wish you the best of luck, but please be aware that the bare minimum necessary study is still a lot of study for a long time.