But, contrary to my suspicions, they apparently don't lobotomise children during the school day - in fact those mood-swings stem from the sheer exertion of behaving while in school, forcing them to explode in a fit of non co-operative exhaustion at the end of the day.
So in a bid to survive this strange and frightening phenomenon, I polled some other mums for their expertise on the matter, and together we came up with these top tips for dealing with even the most savage attack of the after-school grumps.
All the mums I asked agreed that a snack after school is essential for helping to restore your child to its factory settings. Louisa, mum of one, recommends not going near the school gates at home-time unless armed with a snack. "If I feed the raging beast as soon as it gets out of the classroom, I eventually get a lovely little boy to take home." Check out our easy peasy recipes here for extra mum Brownie points.
We've all done it. Your child comes out of school with a face like a wet weekend and you instantly start probing for details and pressing for an explanation for their bad mood. 'Don't bombard them with questions at the school gate,' advises Liat Hughes Joshi, author of Raising Children, a guide to parenting children of primary school age. Instead, try offering a conciliatory hug (albeit out of sight of the rest of the class, if this is likely to cause embarrassment) and then switch the subject to something totally separate from school, like plans for the weekend.
Hit the park
Children are like puppies - you can't give them enough love, food or exercise. And there's nothing like a run around the park after a day of listening and sitting still so, instead of hurrying home, try building in time to let off steam after school every day. Mum of one, Sonja, says heading straight to the park even for a short time puts paid to her daughter's grumps, and gives them both the chance to blow away the cobwebs.
Some mums reckon getting stuck into a task together like homework or reading straight after school is a sure-fire way to help your child leave their grumps at the school gate. My son prefers to do his homework after dinner when he's properly rested and refuelled, but giving him something to do like setting the table or helping me with dinner definitely takes his mind off his school-day woes. (Long may his enthusiasm for household chores continue...)
After school clubs
'Leave them at school,' joked one mum, when quizzed on her tips for how to handle grumpy children at the school gates. But Jill, a mum of two, thinks after-school clubs are a great way to brighten up the end of the school day, and finds her children usually come out smiling.
Have a nap
My lads would never go for this but mum of two, Shannen, says a little post-school nap can work wonders on her daughters' moods. I'd be worried that my boys wouldn't go to sleep at bedtime if they took a nap, but depending on your child's sleep patterns and their age, try snuggling up on the sofa together for a little snooze. And of course making sure your child is getting enough sleep at night will help too.
Or drink water, to put it another way. We often confuse thirst with hunger, and don't become aware of being dehydrated until we feel thirsty, but dehydration can cause everything from headaches to poor concentration and grumpiness. Our bodies and brains need water to work optimally, so encourage children to drink enough during the day, and top them up as often as possible after school. A good indicator of how well hydrated they are is the colour of their pee - the paler the better!
Above all, it pays to remember that children are just like us, but younger. They have good days and bad days. Think of that therapeutic bath or relaxing glass of wine you indulge in at the end of a difficult day - it's our job to help kids form their own healthy habits for unwinding after a long, tiring or difficult day.
What works best for your children? Share your tips below...