ALL kids, MOST kids, say things like that.
It is a phase.
I remember saying stuff like that as a kid.
I knew it was not right.
But as a kid, you say it.
You then grow out of it.
Sure, if you don't want your kids to think this is okay, then you talk to them.
Just talk to them.
It is not complicated.
You tell them it is not nice, it is not acceptable, it is rude, it is mean, it is sassy, or whatever you feel is the connotation of it.
Then you teach them sentences/words to use instead:
"Stop doing that. I don't like it."
"I am going home, I don't like the way you are being bossy."
And if a kid is telling your kid: "If you don't do what I want, I am going home!" Then fine. TEACH your kids, how not to be Bullied. If that is what the kid is doing. Then THEY should go home. Why would you want that kid to stay over, anyway?
Role-play with your kids.
Teach them words and sentences to use.
Kids are kids. And even the BEST of friends, will do that. If play is not going the way they want, they just have to have self-direction and go play with someone else, or do something else and/or speak up. The child CAN actually say "I'm going to play with someone else." And do so. Or "I don't like how you are acting, its mean...." then the child can walk way and do something else.
Yes, the kids DO have a big age difference.
And yes, a 6 year old is also young. They are not grown up either. They have their own, age-related phases and issues.
Not congruent with a 3 and 4 year old.
Also, the 6 year old is not your kid.
Will the Mom actually appreciate your 'teaching' or 'correcting' her kid?
You- ALSO need to teach YOUR kids, that they are NOT 6 years old. Thus, don't act that way. It is not appropriate.
You teach your kids, that that child is a LOT older than them. You need to teach your children too.
So that they learn, how to "Discern" other kids/friendships in the future.
And nothing is wrong with just saying "That child is not nice. That is not proper behavior. Mommy does not allow that. You know that" etc.
Once your kids enter elementary school- this.will.happen.all.the.time
So, its best to teach your kids about how to 'discern' other kids and behaviors, too. Because you cannot 'correct' every kid that they encounter. And THEY have to learn, how to manage too. And how to 'choose' friends. Not just befriend everyone and those who are mean.
It is about teaching your kids. So that they can think on their own.
This is one of MANY phases and things that kids say.
So, it will happen.
And it will happen a lot, once they start school.
That is not your kid.
You should not think you have to correct all the other kids that exist in the world.
You 'teach' YOUR kid. About how to choose and discern and how to manage in life's moments and how to express themselves and have skills.