Just because they posted on Facebook doesn't mean that the actual reason they vaccinated their kids was just to do that. They were lied to by the media and even worse by their doctors. There's a very significant difference between jabbing your kid to virtue signal on Facebook vs jabbing your kid because you think it's "safe and effective" and the right thing to do to protect them and then virtue signaling on Facebook after. One of these is half decent and an attempt at good parenting while the other is effectively treating your child as a prop to carry around and show off. I highly, highly doubt there's any significant group of people who actually do the latter.

Facebook is also a massive minority of nutjobs. It's also filled with bots to push a narrative. So if someone for example posts a picture of their kid after getting the shot and you get dozens of people responding saying they did or are going to do the same, you could reasonably assume that dozens of people haven't actually done this as only the original person posted a picture. The rest could simply be bots keeping the echo chamber alive.

Then there's this person: https://greatawakening.win/p/13zzaW9t5e/its-a-bitter-pill-/c/

They posted their kid after getting the jab but it's exceedingly clear after reading her descent into madness (Read: reality) that she cares about her kid and was lied to by a world that makes it possible to live in a thick, protected bubble that's completely separate from any form of truth. Lied to by the media, by the doctors, by the schools, by other people calling """ani-vaxxers""" "conspiracy theorist flat earthers". By the end, she seems to realize her mistake and likely regret it. If she only did it to virtue signal that wouldn't have happened. So even among the minority of people posting their kids on Facebook and Twitter some among that small subgroup can't even be pinned down as jabbing their kid to virtue signal.

Bonus point, the kid even says "yes" he's happy to be jabbed. Now imagine he didn't get any adverse reaction (in fact, I just reread and he said yes he was happy AFTER the myocarditis diagnosis), he'd grow up into the perfect little drone who's fully submerged in the fantasy world, ready to be controlled and weaponized against the truth. Not because he wants to virtue signal, but because it's all he knows.