I’m trying to understand. If you are talking about in the example of saying maybe how cute or how whatever one child is over another than there’s only one real way of handling it. Build your children up at home. Children only notice differences if they are blatantly outrageous like if someone says one child is cute and then makes a statement that the other(s) aren’t. I would speak up in that instance. However in general I don’t see an issue with strangers saying something about one child over another. This is my personal stance on it.
I have 3 kids. People stop me to say things to them but generally speak to all of them. My kids are outspoken in that if and when someone speaks to one they make their own point to say hello back especially if they see me engage with a person. Not one time to my knowledge have my kids ever said or shown signs of being intimidated or less confident when interacting in public. They can hold their own. I believe in teaching them they will not be everyone’s cup of tea but that makes no bearing on what they bring to this world and who they are. We teach them to acknowledge how they feel but not to let it dampen their light. Someone saying how cute one child is doesn’t take away the beauty of my other 2 children. We stress how confidence, being true to themselves, and finding out who they are makes them the most beautiful even in a crowded room.
I would suggest the same. Strong people have feelings but they can only be broken by a stranger’s quick interaction if you the parent let it go too far. Take charge in how they are encouraged and loved on at home and they will be quick witted in public.