Mom: Let's have an adoption party!
Kid: *cries*
Mom: What's wrong?
Kid: I'M ADOPTED????
Mom: Let's have an adoption party!
Kid: *cries*
Mom: What's wrong?
Kid: I'M ADOPTED????
Okay, listen up, buttercup! The joke is that the mom suggests a party for the kid's adoption, and the kid is all like, "Wait, I'm adopted?!" The humor comes from the kid not knowing they were adopted until the mom brought it up, which is kinda backward. Also, jokes are funny to distract from the sad existence you lead.