Just having a train go in circles for a while can lose its luster over time. One thing I like to do is run a passenger train on one line. Set it and forget it. It will almost always have the right of way.
Then I operate a second train which is almost always freight. I get an engine from the engine facility, go get a caboose from the caboose track and then head over to the yard to build a train. (No hands allowed). This process alone might take me thirty minutes. I have to interact with the passenger train too so I am delayed if it is in the area and must wait for it to go by.
Then I deliver some cars to sidings/industry and pick up empties that have to go back to the yard. I might run around the layout a while, let it run for a while by itself and then start controlling the passenger train to stop at stations.
Then it's back to the yard to put all the cars away. Again, no hands allowed. Then return the caboose and park the engine. Then take control of the passenger train and put those cars away and then park that engine. I can kill a good 2-3 hours doing this.
Then there are times I just run a train, set it and forget it and work on the layout. Maybe scenery, a building, wire something up or fix a problem area that some gremlin caused.
In order to keep my young kids involved when we started years ago, I challenged them never to touch an engine or a train car. It they wanted something, they had to dig it out making lots of moves. That got them thinking and problem solving. It also kept the interest level high. They were doing something with a purpose in mind.
Hope that helps.
Ron