<human>: Hi all, this is becoming a big source of animosity and would appreciate any advice. 

My sister who has no personal experience raising kids (other than helping from time to time with my son) is dating a guy who has  school aged children from a previous marriage.  I've met the guy's kids, and as far as kids go, I think they're pretty well behaved.  If anything they're a little spoiled and clingy to their dad (sisters boyfriend). 

However every little thing is a source of misery when it comes to the kids. She is always complaining about how they're messy, clumsy, forgetful, and how needy they are when they get sick. She hates how they try to do things themselves but get in trouble or break things, rather than asking her for help.  More than anything she complains about the kids' weird personality quirks, like odd habits, and random times they decline doing common sense, "fun" things that you would expect a kid to like. 

My sister, for her part insists that she wants to have kids, and if she could be the parent she would do a better job and the kids would be better behaved. (She feels her boyfriend spoils them, which may be true, but again, they're not bad kids). 

I have repeatedly tried telling her that these kids aren't bad and pretty much everything she is describing goes with the territory of raising children. As we know, kids are weird, and they're not just short adults. But she still is stuck on the issues and doesn't want to leave him either. 

Sooner or later it's going to reach a boiling point and will take care of itself, but I'd like it to work out since the boyfriend is good for her.

Could you distill the essence of the text into 1-3 sentences?
<bot>: Sister's boyfriend's school age kids are driving her nuts to the point of ruining an otherwise perfectly good relationship. But my sister's lack of experience with kids may be causing her to have unrealistic standards for the kids.