Thaddeus Young believes his baby sister is an alien because she says her "Ga gas" in prime numbers. She's the prime baby.

The storyline goes in a direction that surprised me a lot, and I'm not sure how much I liked that. However, I did like Thaddeus a lot and wouldn't mind seeing him in another book. ( )

A typical older sibling jealousy story with weirdly dark elements, though those are the parts that make it more interesting. ( )

This book is adorable and funny. I feel bad for Thaddeus's parents, one of their kids is an alien gateway and the other is a psychopath. ( )

A tween book about accepting change, even if it isn't quite what you expected. A very funny book with some math allusions that are worthwhile.

GN580L ( )

Sibling jealousy with a dark and fantastical element, but still lighthearted and funny. Thaddeus is certain his 18-month-old sister is an alien, proven by the fact that the number of times she "ga-ga-gas" is in prime numbers. He even puts up a YouTube video to prove it. His parents are unconvinced and his school friends think he's crazy. Then one day, aliens come out of his sister's mouth to spread their message of smiles and happy feelings. She is confined to a research facility for observation. Thaddeus realizes she is lonely and contrives to join her and keep her company. ( )