While it may be like learning a second language, I personally feel learning to code in elementary school would be like learning a second language without understanding the concept of punctuation. Now, before getting all flustered, hear me out.
Using a programming language successfully means using math concepts that elementary school students usually haven't been introduced to yet and requires strict formatting control, something they're still working on in elementary school with their primary language. Assigning values to an abstract variable is first introduced in algebra, and order of operations arrives late in grade school and weeks are spent on its mastery. Requiring specific words for a program to work when kids may still be struggling with spelling is another thing that comes to mind. If there is a language suited specifically for the youngins, great, but teaching a programming language to grade schoolers to me is like taking physics before algebra.
The only thing I can think is a cultural barrier here, how far does Australia's elementary school go? Where I'm from, elementary school is up to grade 5, or 10/11 years old.