Well in my line of work (childcare), I find it extremely difficult not to judge as there are truely some crap parents out there!
Having said that, the parent is never made to feel like they are being judged whether I am trying to give guidance or advice, it is always done in an attempted way that is positive and supportive. Some people just don't have the skills they need, others just couldn't give a toss really.
And yes, as far as coke in bottles and smoking in cars with children and not putting children in child restraints in the car, I do judge and I think you;ve got to, who else is going to be the child's advocate?