After some very quick and lazy research, I've learnt that Ruth Belov Gross started writing for children in 1970 with What Do Animals Eat?, and is still creating this stuff for kids. The Laugh Book (1971) is illustrated by Leslie Jacobs, who seems to have started in the late 50's.
I think the simplicity of this book is what appeals to me; the diagramatic illustrations, and the laugh-along dumb rhymes and puns which make it look so easy. Surely if we just sat down and got on with it, everyone could be producing these books! Maybe not as elegantly as The Laugh Book, but I guess it would get easier.