I think you are a bit confused.

Taking a look at perldoc perlvar, one might note that $# is deprecated. This is not the same $#array of which you speak. Your code above breaks whenever anyone bothers changing $[ (perhaps an insane programmer wishing to update your code?). Your code above should instead be written as:

@parent[3..@parent-1+$[]
[download]

Of course, @parent - 1 + $[ is a long way of saying $#parent. So why not just use it?