I think this was from a book or collection of short stories, but it may have been standalone. IIRC the text was pretty big and I read this as a child, so most likely it was aimed at YA or younger. I'm in the UK and so the book was at least printed here - unsure if there was any wording which would have indicated a British or US author.
All I remember is the twist: Written in the first person, a school kid discovers that their entire family are aliens when the family hold an intervention in their kitchen.
It turns our protagonist is also an alien - the intervention is to explain to them that the aliens are on a kind of school trip to Earth, and that some (alien) children can get so caught up in their experiences they forget what they really are.
I think they went back to space and had to leave their new human best friend behind!