Question about vaccines

Ppl are too black and white on this issue so please don't make a case for one or the other. I just want to understand:

You know how some say if u don't vaccinate your kids, it endangers other kids? But if the other kids ARE vaccinated, doesn't it mean they have protection against unvaccinated children?

My baby is gonna start making baby friends soon so I am curious about this and if I need to be cautious