Charming, upbeat story about a dog who is unexpectedly born into a cat family - would be suitable for kids over the age of about 5. As usual with Ungerer, there are plenty of clever jokes for the grown-ups hidden in the pictures. I particularly liked the scene where Flix is celebrating his engagement to the cute poodle in "the best restaurant in Cat-town", and there is a sign on the wall saying "No Dogs". Also the wedding in the cathedral, with a statue of St. Bernard near the altar. But good as this book is, not even close to his masterpiece, "No Kiss for Mother".
Update: four-year-old Samuel visited today, and I tried reading him this one. Possibly my impromptu translation wasn't so good - I find it much easier with Swedish books - but I'm more inclined to suspect that he was bored by the political message. When we reached the bit near the end where Flix founds the UDC (Union of Dogs and Cats) and starts militating for equal rights, he lost interest altogether and went to look at David's Lego set instead. So, probably not a winner for very young kids.