Slop.

I think in this case this argument doesn't really work because the extent to which society trusts toddlers to make decisions about their own bodies is limited (and there's obviously some good reasons for that, but it should be interrogated here). You know, same thing with kids getting tattoos, cosmetic surgery, etc. You generally don't argue about this from the position that children ought to be able to do whatever irreversible thing as long as they want to, because almost no one agrees with that. Not that we shouldn't allow some grace for letting minors make decisions about their health and their bodies even if their parents disagree, which is also a prerequisite for all children (but especially trans children) to be healthy.

If someone asked me, in good faith, if toddlers should be allowed to transition I think I'd answer back with another question, which is why are we imposing gendered behavior on toddlers in the first place? If the caricature that's implied by the tweet, that of some activist parents who "trans" their toddler, is so abhorrent because it's wrong to impose the wrong gender on their toddler, doesn't it stand to reason that imposing gender at all is just as wrong?