I don't understand....

I genuinely don't understand how my partner's SIL can be against vaccinating her children, and has had two babies die from diseases that would have been prevented with the vaccine.....but then shouts about a great low cost clinic to vaccinate her pets, on Facebook..... Why is it OK to vaccinate her pets, but not her children? She currently has 7 children, one inside dog and cat and several outside only dogs.