If there were a formula for people to be funny, everyone would be laughing and the world would be different. If you are a funny person in life, and you are a writer, then you probably can write humor. If you have to ask, probably you should stick to the straight stuff. Now that I'm a parent, I understand why they said that, but I'll still answer any question that isn't in whine format. I'm so busy now though with two other books, a novel I'm writing and my next picture book, that it's too soon to think about that.
Kids love silliness, but so many adults are uncomfortable with it.
People are afraid they'll look stupid. I also think people believe that if they're silly they won't be taken seriously. And people work so hard to be taken seriously. But people take Steve Martin seriously and he's as brilliant and can be as silly as you can get. So go figure.