I never thought a cartoon this old and silly would so enrapture both a 4 yr old and a 6 yr old!!!! They sit spellbound, often not even playing with toys or one another as they typically do while at my house. And they laugh hysterically and would watch for hours on end, if allowed!
Perhaps part of the magic is that this cartoon is just about fun--Felix out smarts the Professor every time and THEY aren't asked to participate, to figure things out...they aren't "preached" at, or given a message of import to learn. It's just...FUN.
Yes, there's random "violence" in the shows...Felix is captured but always escapes. But they've yet to even take note of any of that (ropes, guns, rockets, etc, except for when Felix gets to go to the moon on a rocket--"Lucky!!!"). So far, so good. Just silly old fashioned fun!