Background: My Dsis and I are both in our thirties, and both have children but mine are all teens (the joys eh 
) while hers are only six and eight. She's recently moved back up to Scotland after a decade down south, so in a bid to reconnect I invited her family over for dinner.
The entire time her kids ran riot around my house. I gave them my old tablet to play with as well as some toys/board games and dvds. They started throwing my tablet back and forth to each other until it fell and cracked. Not a big deal on it's own, they're only kids and that's why I gave them my old one. They then spotted my DD's ipad on the tablet and began playing with that in the same way. I took it off them and put it out of their reach, only to come back and find dsis had taken it off the shelf and given it back to them!? She started laughing and said that they're only kids and they'll throw a tantrum if they don't have anything to play with. She assured me she'd keep a better eye on them, so I relented and gave it back to them.
Not ten minutes later there's a huge crack across the screen. 
After dinner I put on a DVD for them while my Dsis and I sat on the sofa and had a drink. I stepped into my bedroom quickly to take a five minute call from my boss, and came back to find that her kids had went into my DS's room and picked all the keys off his £150 mechanical keyboard and spilled juice all over it!! I shooed them out of the room and they ran into the kitchen where they then started opening up all my cupboards and began pressing all my amazon dash buttons. They order eight lots of toilet paper 
These are only the examples that cost me money, but they spent the entire night being unruly and my Dsis did not lift a finger to keep them in line. It's left a really sour taste to what I'd hoped would be the start of a closer sisterly relationship. My kids were at their dad's that night so didn't witness the carnage first hand but came home gutted to find that their things had been damaged. When I attempted to discipline her kids myself, Dsis accused me of being a b and a child hater ??? Another gem from her was the line "you have kids, you should know not to put those buttons where kids can press them." My youngest is 14, and is perfectly capable of opening a cupboard without pressing every button in site!!
AIBU to expect her to discipline her kids at my house? I know my kids are all older, but I'd never have let them behave like that in my own home, never mind someone else's!