Depends on who or what catches it. For instance, If one of the viruses catches your child, The cost could be paralysis, Deafness, Brain damage, And even death. Basically, You would be lucky if it was only CPS that caught you.
Back when I was a baby, Late 1970's, They didn't have an approved vaccine for whooping cough. My older siblings caught it and of course gave it to me. Seeing I was still only months old, My lungs weren't strong enough yet to cough up the mucus so several times a day (and night) I would stop breathing until they shoved a tube down by little throat to suck it out of my lungs. From what I'm told, I turned all kinds of colors in the process. One of the nurses (a nun) was so concerned about my condition that she pinned her Rosary to my pillow. Thankfully, I can't remember any of it but from what I was told, I came moments away from death several times a day for about a month. I can't imagine the emotional strain it put on my family, Especially my parents. Knowing that each night they left the hospital, If they would get that call in the middle of the night. But hey, If it sounds like a risk your willing to take, Remember, It's not just your money your putting at risk.
This is either an uncreative shitpost or a blatant strawman question. Either way, I would prefer to believe that the child suffering from nasty nasty diseases would be punishment enough for the parentses.
There should be no fine. Some people with compromised immune systems cannot safely have vaccines, Which is why the antivaccine movement is proving so dangerous. However, There should be limitations on how children whose parents chose not to vaccinate their children move through society. E. G. No public schooling, No public transit, Perhaps even fines for something as simple as shopping in person at the grocery store without a hazmat suit on (only kidding a little ;-). However, It is not the child with ignorant parents that is at fault. It is society, The educational and medical systems, And most especially, The parents of the unvaccinated (without just cause) child.