Have you seen the symptoms and complications of these diseases? The odds of a side effect from a vaccine are much, much lower. Few things in life are entirely risk free (not even sleep).
And truthfully, that's not even calculating in what happens when the very young, old, pregnant or immunocompromised folks get these diseases.
They were known as childhood killers for a reason. They still ARE in some places and watching kids suffer and die is pretty horrible. There's even videos on youtube of patients with these illnesses and it's awful.
Usually, we need herd immunity to protect those who cannot get vaccinations. When herd immunity fails, it's not pretty.
If the two girls were full adults, they would have legal agency. They do not, and as such, the decision falls to their legal guardians. Unfortunately, in this case, a spat between the parents made it into a legal case. That's pretty much the reason this even came to court. And really, I have yet to meet a kid (or adults for that matter) who enjoy getting the shots. I suspect they'd enjoy the disease much less.
And no, you don't have to treat kids like things. But their brains are still developing.