How about Brio type trains, especially for very young children, and economical electric trains (Postwar Lionel, KLine or LionChief/LionChief Plus) with adult supervision.
The Brio trains are great for children to play with any time, no supervision necessary. I agree that they are great for young children's imaginations, creativity, mental development, etc.
Then, the electric trains are for special times, with dad or mom. That engenders bonding, joy, learning, fires up the imagination, etc., like it did for many of us when we were little kids. Arnold