Forget the ground hog and various presidential birthdays; February must be Temper Tantrum Month! I have grouped your questions, Cathy and Pascale, not to slight you, but to reassure you that you are not alone in dealing with tantrums. They occur in all preschool children at some time or other, and in some children they occur a lot of the time. Of course, children are enormously clever in staging them at times and places that will cause you maximum embarrassment.
It may sound like I am begging the question, but the most important thing is to prevent them if at all possible. Temper tantrums usually don't appear out of the blue; most children put out storm warnings—whining or looking unhappy, having a request turned down, tensing muscles, pushing or throwing a toy. If you are in the same room and can read these signs, quickly spring into action. And your best ally is distraction. Act as though you don't see the signs and say something like, “I'm tired and would like to sit down. Would you like me to read you a story?” Suggest a walk, or a snack, or anything other than what he is now doing.
If you can't prevent it, then ignore it as completely as possible. Get him to a place where he can't hurt himself or a sib (or you) and say, as calmly as you can muster, “When you've calmed down you may come out.” If your mother-in-law is there and suggests something else, say something sweet like “I'll try that next time.” If it happens in the check-out line at the grocery store and the clerk or someone else in line glares at you, say, “"Did that ever happen to you?” Try to look away from your child as you say it, but try to position him so he can see the look on the clerk's face!
Our parenting advice is given as suggestions only. We recommend you also consult your healthcare provider, and urge you to contact them immediately if your question is urgent or about a medical condition.