I once did an object lesson for my Sunday School class that was effective.
I had left-over mashed potatoes, and I
scooped them into a dish with an ice-cream scoop so that they looked like
vanilla ice cream.
We talked about keeping the Sabbath and likened "Sundays" to "Sundaes" and how when we do the things we should, it was like adding extra toppings.
I brought out the dish of potatoes and while we talked about the things we shouldn't do, I topped it with things like ketchup, mustard, etc.
Of course the kids all thought it was ice
cream so they were having fits. I asked them to think about what they would like
to have on their ice cream and about which type of Sunday/Sundae they would like
to offer the Savior. I did eventually tell them that it wasn't ice cream......
I also had a counselor do a ST one time on sort of the same subject.
She actually built a nice Sundae and then at the end sprinkled dirt all over it instead of sprinkles.
The kids had fits over that as well, but the object stuck with them. The above lesson did as well. They both take a lot of thought.