I guess it depends a lot what we mean exactly by 'hierarchy' here.

Like you shouldn't look at kids as your buddy or equal in the sense that you're on the same wavelength as them. But equal rules and standards would apply.

Like to me a non hierarchical relationship is you guide them and help them and show them things. (It would still be mostly similar to the traditional "parent" role.) But there wouldn't be bedtimes or things like that (there wouldn't be hierarchy in the sense of I pick the rules everyone lives by).