Yes, I would have judged.
No, I wouldn't have been in Primark in the first place. (I've been in once, but came over all peculiar and had to leave)
Thing is, though, IRL, you tend to have more context available to you to decide if you're right to judge or not, no? Because you don't just look at the children, but also the mother, the condition of the clothes, whether or not the family seemed happy etc etc. Then you judge. (or not)
What I don't get, is the incessant need to start thread after thread about other parents we perceive to be inferior to ourselves. I judge a bugaboo just as I judge a sausage roll in all honesty (a friend of mine has just bought, not just a bugaboo but a shocking pink one- ick ick, and my first thought was "Sheesh, what a chavtastic pram)
On t'other hand, yes, maybe the mother in question was a shit mother who only has children for the benefits and the plasma screen and all those other things we are constantly told about. So, yes, if it's proof proven she's a shit mother who treats her children badly, then yes, we should fvcking judge. And how. But only when we know.