It's a tough one.
I can see how the term came about. But I feel there should be an alternative that is kinder to children. They are here because the parents decided to have them after all. I also feel the historical context in the German language can't easily be shaken off.
Words matter. They both reflect and form attitudes. They can erode values. Words are used to turn entire groups of people into "others". We should be careful about the words we choose and consider individual responsibility instead of being swept along unthinkingly.
"Non-parent" would perhaps work? It refers to parenthood status and doesn't imply anything undesirable about children.
The problem with both "childfree" and "non-parent", however, is that both terms define people based on their status relating to parenthood.
Would "adult" or "adult human" be too nebulous?
Is there a teeny tiny part of people who are not parents, by choice, that wants to be provocative or to rile up parents or to imply a judgement on them for breeding, out of vanity or because of some other perceived flaw? Why the need to use a term that comes with a good deal of baggage?
I am aware of a very strident community online (referred to by a PP) that is actually very anti-parents, and sadly and worryingly anti-children - yes, I agree there are shades of the incel movement there in both content and tone.
Again, it's important not to sleepwalk into terminology that has negativity at its heart.