Parents need to know that all kids may enjoy this book (which was made into a movie in 2011), though it seems aimed at kids older than recommended by the publisher. Parents may need to explain the more obtuse language as well as some of the darker cartooning. Also, the idea that Martians could kidnap a kid's mother might unnerve some.
Positive messages:Mom shows unselfish love for her son and he learns what is special about moms.
Violence & scariness:Moms are nabbed by Martians, but no real violence is shown. Milo and his mom almost run out of air on Mars.
As an adult, I loved the pictures and laughed at the story. I knew from reading the review here that my 4-year-old son was probably too young for the story and he was. He was scared about Martians coming into the house to take moms and worried about it for the rest of the night. What surprized me was that my 6-year-old son, who I read it to separately, was also scared by the idea of mom-napping and the peril of the humans gasping for air on Mars. Afterward, he told me that he didn't want to hear it ever again. The Martians are colorful and funny-looking, not scary, so I never expected it would be so scary to them.