I have read 5-30 children's picture books a week for almost 9 years now, so I'm pretty much an expert. There are classics that will always stand the test of time- Goodnight Moon, The Little House, Llama Llama Red Pajama, Ferdinand the Bull. But, if you read other books by these authors, they don't quite have the same mix of comfort and surprise that makes a good short story. Or it's the same plot with different characters.
One of the things that is challenging with kid's books is that you, the parent, have to be able to read them over and over again without wanting to claw your eyes out. The kids have a book called Who Stole the Cookies From the Cookie Jar where every page she asks the titular question and the protagonist guesses an animal, who then explains that they didn't do it because they eat grass, or flies, or antelopes. At the end, turns out it was the ants who stole the cookies, but they stole them to set up a party and invite all the animals to eat the cookies that they just explained at length that they don't eat (WTH?). The kids love it, but I hate it, so I hide it on top of the bookshelf where they can't see it.
To make books interesting for parents, authors will often try to be clever, like in the Amelia Bedelia series. The problem is that with EVERY. SINGLE. PAGE. you have to spend 3 minutes explaining the joke... that pare is a word that no one uses that means peel, so when Mrs. Rogers says "pare the vegetables" and Amelia Bedelia "pairs" the vegetables, it's funny... see? Times 20 pages.
It also can't have too many words on each page or be too long because either the kids will pick it to drag out bedtime, or it won't hold their attention. Cloudy With a Chance of Meatballs has this problem- it's original enough that it takes like 15 pages to explain the premise before getting to the actual story, which is fun and all, but I just want my kids to go to bed already.
However, there are two authors that I can think of that overcome all these difficulties:
Peter Brown and Oliver Jeffers. Every single book is just right: just the right length, just the right number of words per page, just the right amount of clever, beautiful illustrations. And every book is good.
Although I love them all, my all time favorites are-
|A bear finds a boy in the woods and takes him home.|
|A little boy gets his favorite shoe stuck in a tree.|
If you are wondering what books to get your kids/niece/nephew/grandchild, buy them these.
Or, buy them for yourself, because they are great.