Life is so hectic that delayed gratification is not as high on my list of priorities as I wish it could be. When I tell Alex that he needs to wait, I do it out of necessity rather than as a teaching tool. However, I do think that delayed gratification is extremely important and I really like the experiment mentioned in this letter at All Financial Matters from a mother to her daughter about saving for retirement:
When you were a little girl I did an experiment with you. You didn’t know about it. I put a marshmallow on the table and told you that if you waited for 10 minutes until I got back and didn’t eat the marshmallow while I was gone, I’d give you two marshmallows when I returned. But if when I came back you had eaten the marshmallow, I wouldn’t give you a second one.
What did you do? You waited until I got back. And then I gave you two marshmallows which you promptly devoured with a big grin on your little face.
I’ll probably wait until Alex is a little older to do this with him, but I think I’ll do it repeatedly over time (varying the reward) to reinforce the point that good things are worth waiting for.
Note: The letter is long but worth reading and using as a model for your own letter to your children.