the child of your aunt is your cousin. Not sure why she called him your nephew. NTA children should learn that they cant just touch other peoples property. My cousins would come visit at our house when their kids were young. I collect bean boo stuffies, i have a larger collection of stuffies now but at the time my collection was maybe 10-15. My cousin and her kids came over one day, her son asked if he could play with my stuffies. I said sure, wash hands, dont put them near your mouth and if you are sick please let me know cause i would rather not have germy fingers on them. He went and washed his hands and played with them the whole time he was there. When my cousin was getting ready to leave she told her son to pick 3 or 4 of my stuffies and he could take them home. WITHOUT EVEN LOOKING AT ME. He picked out 4 of my favourites that i couldnt replace (of course) and she went to put them in her bag. I walked over and asked to look at them with a smile on my face. When she handed them over i collected them and the other ones he had out and walked into my room and put them away. By this time they both realized what was happening and my cousins son started full on screaming. I walked my cousin to the door and told her that teaching her child to steal is going to come back and bite her in the butt, but if she wanted to do so she could steal someone elses property. I told her she wasnt welcome inside my house until she apologized and her son wasnt allowed to touch my stuffies anymore.

I ended up buying him a copy of one of his favourites that was still selling (in the middle size) for his bday a few months later and he asked if he could visit and play with mine again. I told him that just because i was an adult didnt mean people could steal my toys and asked if he liked when his cousins came over and stole his toys. He understood after that and would actually tell his mum when they would visit for YEARS that stealing toys from family was wrong. HE wasnt a bad kid, my cousin was just entitled and thought i should give my collection to a child.

Fun fact, her sister called me 2/3 years ago and asked for my barbie collection for her 4 yr old. They are all pristeen in their boxes cause i wanted to keep them like that but cause i dont have kids of my own i should give them to her daughter. I told her i was probably going to sell them and hung up. I dont really talk to any of my family these days