Not at all.
Both of my children are very well behaved and well mannered. (The youngest has always been a little shy and reserved on first meeting or when places are busy and overwhelming, or if someone appears particularly intimidating, but with patience he is beginning to flourish. His teachers describe him as a role model for other children and a pleasure to have in the class. So he's not rude or impolite).
However, I am also and have always been, forgiving and understanding of tiredness, shyness and all the other things which impact small children. Children have to learn behaviours and how to regulate their emotions and how to interact. It takes time and they are all on a different time line.
When I was growing up, I lived in fear of my mother. I was exceptionally well behaved because if I was not to be, the consequences would have been horrendous. I don't think that's helpful. My own feelings and emotions were never considered. In her opinion children should be seen and not heard. Forgetting a thank you or to shake hands with someone on first meeting, was a huge no no and seen as a bad reflection on her. Really, her view was that my behaviour was always a reflection of her. She wanted to be seen as having wonderful, happy, polite, well adjusted, perfect children because she thought it made her look superior and perfect. Much like, perhaps, some on this thread.
With my own children, I try my best to instill manners but I also try to understand what they might be experiencing and why they might be acting in certain ways on a given day. I also make a judgement call about how and when I discuss behaviour with them, and don't always do this in front of others parents for good reasons.
I love taking my children to visit people who I believe to be my friends and who I believe won't judge me, because if I'm relaxed and my children are relaxed, we will all have good time. I hate visiting people or seeing people who judge. It puts me on edge and I worry.
I have noticed that a lot of those who judge are in fact quite insecure themselves or think themselves superior in some way or somehow believe that their perfect children will make them seem admirable. It's a shame they can't relax and learn to be more supportive of fellow mums and friends.