I'm so pissed

Because there's this fuckass toddler, he's my cousin or wtv he is I don't even care enough to know and he's so DAMN ANNOYING "Roma why are you mad at a 4 year old?" now my first reason is pretty dumb but he keeps coming into MY room, annoying me and snatching my stuff while laughing. And my bitch of a mom is like "well maybe if you let him stay in your room he wouldn't be doing this to annoy you! You were the exact same as a kid but I didn't let you get bullied!" JUST BECAUSE I ACTED LIKE THAT IN THE PAST DOESNT MEAN I SHOULD ALLOW OR THINK ITS OKAY. And then he just wont LEAVE, and my mom is always in the living room either asleep, awake, or on the phone and she'll watch him for about 3 seconds before just not caring.

Reason two which happened today(also my cousins mom dropped him off for a WEEK), so I was outside playing with the kittens right? BUT THE DUMBASS KEEPS BOTHERING THEM WHEN THEYRE TRYING TO WALK AWAY AND I ALWAYS LEAVES THEM ALONE WHEN THEY DONT WANNA BE BOTHERED. But a few minutes later cuz my mom was also outside with him on the phone so I expect her to keep watch of him while I'm taking a break but no, I played with the kittens for a bit and they ran to their mom to get milk but ofcourse the dumbass runs over to them, he only watches but when the momma meows the shit SQUEALS, AND SCARES THEM AWAY TWO TIMES. TWO TIMES OF SQUEALING, another hour passes by when I went back in the house, I played with them again only to see the DUMBASS HITTING THE MFKING KITTENS, I push him away and he's LAUGHING. I drag him to the backyard with the swings and my mom was there too ON THE FUCKIGN PHONE NOT EVEN WATCHING HIM. But he ran back and I was playing with the string with the kittens but the little shit PUSHED THEM up under the car, not even gently. AND I PUSH HIM TO THE BACK AGAIN CLOSER TO HIM. I go back inside cuz its hot as hell but when I come back he was literally pushing one black kitten into the wall(kinda squishing them on it) while laughing, and I'm trying my hardest not to hit him or commit murder to a toddler, I drag him to the back finally telling my mom to watch him because he's been hitting the kittens. She holds his arm for THREE, THREE seconds before letting go, I keep a watch on him and he hits the kittens again laughing and I turn back to see my mom watching on the phone before turning around...ARE YOU STUPID? BRAINDEAD EVEN? And I'm just standing here wishing the most painful death upon them both(I really hate that I do that tho because that's mean)

Am I overreacting? because I've told him to stop because its hurting him MANYYYY times, he's even got a whooping from my mom and he is STILL doing it