Hi Brie and Tina,
 
Thank you for your questions. 
 
Tantrums can be the most exhausting part of parenthood.  Some kids are just little gladiators.  They fight over everything from morning until night.  They scream "No" to everything you ask them to do and can literally take us to the end of our rope. The most important thing to remember is that yelling never works.  It only escalates the situation and makes parents feel terrible in the end. 
 
Some kids can tantrum multiple times a day and those tantrums can last well over an hour.  Other kids experience what I call mini meltdowns several times a day (crying, sobbing and falling apart over various things).  Still others are oppositional and every request from put your coat on to come to dinner is met with a loud "NO!"
Believe it or not, there are some tried and true ways to deescalate and drastically reduce these tantrums and oppositional moments.
 
The most important thing to remember is to stay neutral.  Don't yell and don't scream.  My book, Connected Parenting, will help walk you through the how to's of dealing with tantrums in more detail, but for the purpose of this column, here are some quick tips.
 
Kids tantrum for many reasons.  But it's the "I want my way" tantrums that are often the most challenging - like the one you describe with the shopping cart and what happens when a child who doesn't like to hear the word no, is told "NO."  These tantrums are particularly aggravating because often what our child gets upset about to us (such as who pushes the shopping cart), is such a simple thing to get upset about and there is the added frustration of it all happening in public. Tantrums that seem to us to have no sensible reason, often occur because kids are over stimulated, tired or hungry.  Making sure that our kids are rested and fed and have not done too many things during that particular day may help a trip to the grocery store go much better.  As well, you'll want to make very clear ahead of time what behaviour you expect and what will happen if he misbehaves.  For example, if he gets upset about who pushes the cart, he will have a timeout with mom or dad at the front of the store or you will all leave if it's somewhere he wants to be.  Then be prepared to follow through.  Make sure to try and involve him in the process of shopping by giving him some jobs or some things to think about so he becomes invested. Make sure you catch him being good and making positive choices. 
 
These tips from my website should also help:   
 
It is important to recognize that we can become part of the problem by providing our kids with an audience and a target for their display of emotion. They need to learn that they can soothe themselves, and that they can and will recover from whatever they're feeling. There are some important things you can do to handle a tantrum effectively which will help your children learn this very important lesson:

Try understanding first. Always start by empathizing. This can be very de-escalating and can often stop a tantrum in its tracks.

Never give in. It is okay, as a parent, to change your mind or reevaluate your decision, but never after your child has been rolling around on the carpet in a rage. Say what you mean, mean what you say. If you give in to the behaviour, you may have dodged that tantrum but you've guaranteed another.
 
Don't be afraid of the tantrum. Be neutral and confident. Children watch us, and if they see that we are having difficulty controlling our behavior they may feel it just can't be done. So, the more you yell, the more hysterical you'll both become.

Disengage. Children know when we are worried, if you are thinking "oh please let this work, I hope he doesn't have a fit" He will know it and he will have a fit. Try to be confident and believe that you will handle it. Don't work so hard. Sometimes we become part of the problem. We start negotiating, pleading, cajoling and then threatening. All of which are fuel for the tantrums fire. In a neutral way, walk a few steps away and give what I call paradoxical permission... "Go ahead then get it out. Have a good cry if you need to, but mommy is pushing the cart."

Give messages of competence. Say things like. "You will be fine, you will feel o.k. in a few minutes, you've gotten through this before, and I know you can do it."
                       
If you follow these tips plus some of the mirroring techniques I describe in the book, what you will find is that in a short time, your son's tantrums will decrease, he will recover faster and eventually his tantrums will become far less intense.  Helping him learn that he can regulate his behavior and that he can recover from these episodes will give him great confidence and will make the trip to the grocery store or saying "No" a much more pleasant experience.