JUST when things were going okay and I was starting to enjoy the school holidays (gasp), my daughter dropped a clanger of a tantrum which brought me right back down to Parenting Earth.

I thought my days of tantrums were over, I’ve been five months free of embarrass-mum-in-public moments so I was gobsmacked by her performance yesterday.

Fortunately my son was being lovely which mysteriously always seems to happen whenever my daughter is in trouble and vice versa. It’s like children get a kick out of seeing another in Big Trouble. And, believe me, Big Trouble is not a place you want to be when I am feeling hot and bothered on the way back from the park.

It all started with me talking to my son about getting him a bigger bike. It was an innocent enough conversation, a nice chat, but I was forgetting that his sibling was present and there is no greater force than SIBLING RIVALRY. In fact, sibling rivalry should be remarketed as a weapon of mass destruction. Sibling rivalry could launch a rocket to the moon.

As soon as my daughter got wind that her brother might be getting a new bike, she went mental. And I mean that crashing to the floor, screaming like a banshee, shouting “You are a stupid Mummm-eeeee!!!!” kind of craziness that always happens in public, especially when there’s an audience. Plus we were crossing a road when it happened and she decided to stop slap bang in the middle of it. Thankfully my son was being a sweetie; otherwise I would have just laid down in the road next to her.

Now it takes a lot to make me shout. I have to be pretty much at boiling point, but I bellowed so loud that the Olympic Stadium shuddered. “Ha!” she said, putting her hands over her ears, “I can’t hear you.” So you know what I did? I dumped her scooter in the nearest hedge, grabbed her hand and marched down the street, hoping her body would follow, all the way home and into her room. Which might sound a bit harsh, bearing in mind that it was MOSTLY MY FAULT.

A better mother, you see, would have predicted this tantrum. Any promise of new stuff to a sibling is bound to cause a major freak out in the other child. But being in a glass-half-full sort of place, I thought everything was going swimmingly. Mentioning a new bike in front of a sibling is the equivalent of holding a bacon sandwich in front of a recently turned vegetarian. Needless to say, my glass is now very empty and very smashed.

So after recovering from my post-traumatic stress, I have decided to analyse the situation and have come up with the following formula for the rest of the summer hols:

SIBLING RIVALRY + UNTHOUGHTFUL MOTHER = TANTRUM = PARENT LOSING THE WILL TO LIVE

Which will be handy to know when the new bike arrives next week.

Follow Claire on Twitter @MinistryOfMum