I'm a parent who watches other kids including my own DC. Generally their behavior is better than DC's. However there are children I no longer volunteer to watch-those who go where they want without telling, hopping up from the unfinished meal and doing something else or engaging DC in unacceptable behaviors. Just a few examples.
OP-watch the well behaved children and tell the parents who DC have problems what you experience. Sometimes I think we don't give other parents enough compassionate feedback.
BTW, I'm an older parent who is seen as strict by others- just old school in my view!

The OP sounds like an older lady. She talks about grandchildren.
In all honesty, I have had the same experience with younger children today. As a casual observer, it seems to have started with kids not sitting at the table in restaurants. I don't watch the children in my neighborhood, but it is not unusual to see temper tantrums, hitting other children as well as their parents. I was talking to one young mother and she picked up her child and the child wacked her in the face repeatedly. The mother said nothing
I know there are sweet, well behaved children in our society. I observe less and less of them. Such a broad generalization is uncomfortable for me. However, I can see what the OP is saying.
This conversation may hit a sour note with younger parents and put them on the defensive. I hope it proves to be constructive.

Did you tell the mother how her daughter behaved? I am wondering if there is some sort of issue behind all this, because while some kids do just have days when they're stinkers, my kids are definitely better behaved for other kids than they are for me. (Well, usually.) And yet we have neighbors whose kids don't listen to anyone but their parents. It's odd -- my kids' friends are also usually better-behaved on visits than at home, and I assumed that was standard, until the neighbors' kids blew that theory to bits.

I am the OP. I had children with "strong" personalities. We dealt with behavior issues, but my kids were never this angry. They were difficult at home, but teachers and neighbors sung their praises.
No, I am not having rose colored memories. And I am not exaggerating.

You've gotten used to not having kids. Not saying their behavior is completely normal as you described it but I wonder if your description is based on your rosy "memories"?

My neighbor is a sweet lady, but her kids are monsters. She asked me to watch them one day and one of her children is beyond difficult. I tried to do fun things that I know she likes....color, playing with dolls, going to the park. She ripped up the paper, threw the crayons, licked the dolls and threw them. She threw a small bench at me and at one point told me her friend was going to die and I was going die. I got so frustrated that is made her go to the park. At the park we ran into another mom. Atthis point, I was ready to give this girl back to her mom and put my head in a pillow and scream! The other mom said she has seen this little girl behave the same way with others, but tones it down when her mom is around.

On another occassion, I welcome one of my husbands cousins with her young daughters into my home for the weekend to see the cherry blossoms. Her 4 year old daughter did to talk, she screamed. She did not walk, she ran. She threw things, broke things, hit us, etc..

On another occasion, a young mom from my church asked me to watch her kids because she was in a pinch. This little girl called me "hey you". She was very defiant. If we tried to do something, she refused.

What is going on here. Yesterday, my neighbor asked me to pick up her child and I said no. I would love to be able to help her out, but her child's behavior is unfortunate. I would love to help out a young mom. Her husband travels a lot, just as mine did, and we lived in a neighborhood where we helped each other out.

This is so troublesome to me. I don't have grand kids and I pray my daughter waits. What is going on?