Well, apparently they were back then and still are today for people of all ages.
Coloring books for adults is an offspring of art therapy which is a mental health profession that is the process of making and creating artwork which intends to "explore feelings, reconcile emotional conflicts, foster self-awareness, manage behavior and addictions, develop social skills, improve reality orientation, reduce anxiety and increase self-esteem" (according to the American Art Therapy Association). So basically, it's similar to good old therapy. Also, art therapy is not only about mental health and improving yourself - it's a form of personal expression, as well.
I can recall vividly my father introducing me to coloring in sheets as a hobby, and now I am doing the same with my child. Never mind how the world changes, our children nowadays love to color in just as much as we did when we were young. Kids love to show off what they can do by using their paints on the coloring sheets you give them.
My kids turn into saints once they see the coloring sheets rolling out of the printer. They love it when I start passing out coloring printables with their favorite characters on it. The most valuable aspect of coloring pages are there educational value. They will help your kids with their motor skills i.e. finger dexterity, eye-hand coordination as well as increase their mental capacity. The list goes on regarding the benefits of allowing your child to color versus playing video games or watching television.
That said make sure that the kid prints those coloring pages on a used sheet of paper and tell the kid not to waste paper. That way you will also make sure that he grows onto to become and environmentally conscious individual.
Older children may become bored with coloring and prefer to create their own images. This is a natural progression, and one parents should welcome. Nevertheless, coloring does have a place in child development and can become part of his or her daily routine. Some children may have difficulty expressing themselves; however, as they continue to be creative they will often start to open up more readily. Colouring is a great way to express themselves and their ideas, particularly if they have problems they do not know how to cope with. It is used to bring subconscious thoughts to the surface and help children to understand them. You might not realise it yet you are helping the environment as you do not need paper to draw and colour images.
When I was a young lad not a lot older than my son is now, I began using coloring sheets as an activity I could do with my father. I really enjoyed working on them but I also enjoyed the one on one time with my father and having something we could do together. So you can imagine how keen I am to continue this tradition and now begin having fun with my boy and some coloring pages.