First off, the title might not be 100% correct.

Secondly, some context. I dislike children. They are noisy, tiring, and don't listen. Now, I am aware some people say you get so much satisfaction in return, but I simply do not feel this kind of satisfaction.
Besides this, I still live with my mother. I was planning on moving out soon when my father died and decided to stay with my mom so she wouldn't have to be in the house all alone. This was even more the case due to the fact that during the year before my father's death my third brother moved out.
It's been a few years since and the housing market has gone to shit. I'm forced saving up for about 4-5 years and since I only started working full time a year ago (finished my studies) I have a few more years to go.

Now, the situation. My eldest brother has 2 kids. My mother takes care of them every week on a thursday, and this weekend without discussing it with me first, she decided the kids should stay over. No big deal, a bit annoying I need to move about my evening plans (sleeping in the room across from my room, I sometimes am a bit noisy later on in the evening with music and chatting) but it's all good.

Now, I'd like to say I'm never nasty towards the kids. Although I might dislike children, that's not their fault, so they don't need to notice directly that I dislike them. I help them out, hold their hands outside, etc. etc.

Over the past year the eldest (6 years now) has become a bit more obnoxious. My mother loves to spoil them, whilst I'm a bit more strict. She let's them do whatever they want, turning them into rather spoiled brats (genuinely, my eldest brother says the kids are rather tiring when she returns them, but accepts it because 'That's what she's a grandmother for', her favourite phrase as well.)

As a result, sometimes when I say to them they shouldn't do something (making a mess just to make a mess for instance) she dismisses me saying "Let them be, they're just kids." At some point I confronted her about it, that she was diminishing my authority over the kids by acting like that. To which her reaction was that she is the boss in the house.

Today we were eating pancakes, and the eldest kid decides to start throwing the bottle of syrup off the table, to which I stirnly tell him not to do that. His reaction: "You're not the boss, grandma is, I don't need to listen to you." and he then proceeds to throw it off.

So I lower myself to him to be eye to eye but not bowing down (which is intimidating to kids, so never the right thing to do) and tell him sternly that he should listen to me as well. My mother is 2 meters away from this completely ignoring what's happening.

A few moments later she asks me to watch over the kids for a bit, which I decline, because she has ruined my authority, making my watching over them useless since they won't listen anyway. Now she considers me an asshole for not wanting to help her out taking care of the kids.

AITA?