Xavier sat back in the chair in the quiet place, and tried to keep from laughing as he watched his brother shrink before him. He slipped him a shred of cloth to wrap around his small body as he hid under the table. Then he tried to stay "normal" as he began to read a comic book. One about Ant-Man, a superhero that helped he and his brother start to figure their power out.
And poor Xander had to wait for their first victim. The prank wouldn't work for long, so it was best to do it before everyone knew about them and their powers.