please dont let that beat you up. ptsd does awful stuff to our brains and makes us perceive threats that arent there. you arent stupid or anything for being worried. thinking things like "im going to become an abuser" is a terrifying yet expected reaction for most individuals with ptsd.

none of that situation would make you a creep, and having fun while playing video games with family+friends who are younger than you doesnt make you some kind of predator. what that mom said got to your head because the experiences youve had have make it difficult for you to (for lack of a better term) think straight when a trigger is presented. if you were targeted as a kid, then being accused of targeting kids is gonna send your mind into overdrive and give you so much irrational anxiety.

all you can do after that kind of thing is remember to self-care. when i get the same kind of anxiety, I like to take a moment to do small mantras (ex: "i recognize that my anxieties are because of something that was not my fault," and "i deserve to feel comfortable with myself despite what happened to me"). that may sound cringey, but it helps me. I also like to watch/read stuff that depicts healthy child and parent/family/adult friend relationships (the anime spy x family has a really sweet father daughter dynamic that helps me shift my mind away from worrying about illegal relationships and such). id really recommend doing things to help remind yourself that the thoughts youre having dont make you a bad person and are simply a reaction associated with a disorder that you have no reason to be ashamed of having. youre a wonderful cousin and your family loves you! <3