While I don't doubt that the majority of the spike is illegals, I wouldn't count out a growing anti-vaxx sentiment in the general population. Anyone paying attention is forced to conclude that, at best, public health has little to no evidence informing them of anything they do, including childhood vaccination.

I stopped taking my kids (albeit older) because every shot I research seems to be pointless. Even meningitis, which is pretty serious, only seems to protect against the targetted strains while, at the same time, increasing the prevalence of the other strains to the point that you're more likely to get the disease if you get the shot.

I'd also like to point out that things like chicken pox, measles, and even polio, are dangerous to adults with no immunity but pose little risk to children. If mostly kids are getting these diseases, it's not really a big deal. Of course, they always try to make it look worse by including infants, who are at a higher risk of serious complications.