Have your offspring ever caught you saying — or doing — anything you and the other half shouldn’t have been saying — or doing — in front of them?

If so, be afraid — be very afraid — if your little ones are going to be appearing in one of those free-form improvisation nativity presentations that seem to be catching on.

Witness the unscripted interchange between Mary and Joseph, as recalled by schools inspector and former teacher Gervase Phinn in his book A Wayne In A Manger (Penguin).

He says: “There was the time when the little boy playing Joseph strode confidently onto the stage and asked the small figure in blue who was cradling her baby, ‘And how’s our Jesus been today, Mary?’ ‘He’s been a right little so-and-so!’ came the blunt reply.”

“Or the time Mary announced to a crestfallen Joseph: ‘I’m having a baby, and it’s not yours’.”

And as any teacher or parent involved in preparing for a Christmas presentation will tell you, children always give a valuable, fresh insight into the story that the rest of us might think we know pretty well.

Such as the little girl who offered Phinn a pearl of wisdom and a boy in the same class who gave him a modern reflection on the situation faced by Mary and Joseph. Phinn was explaining to their class that there was no room at the inn, leaving Mary and Joseph no choice but to stay in the stable with the animals amongst the hay. The confident little girl piped up: “Well, they should ’ave booked in advance. It always gets busy at Christmas.”

Undeterred, Phinn continued filling them in with more details, and finally reached the denouement by telling the children that Mary had to have her baby in a cold, dark barn. So the baby Jesus had no nice, new clothes, no toys, no cot. He came into the world with nothing. He was one of the poor and mean and lowly.

Phinn said: “Matty, who had been watching with eyes like saucers in his pallid face, shook his head slowly and said quietly, but with feeling, ‘Poor little b*gger’.”

But what about when the big day arrives and lines have been learned, songs and stage movements rehearsed and actors kitted out.

One big problem is competitive parents, where points are picked up depending on who has the best costume, the most lines in the play and the most time on stage. If your child has secured one of the more modest roles, don’t be tempted to confide in a friend that your son has made the most of his small part, ‘just like his father!’ On the subject of the best costume, don’t be surprised at how liberally the teachers in charge of the production interpret the wardrobe requirements. Chances are that in your day a tea towel and a dressing gown would have sufficed for any of the male roles, with a few sequins making the Magi stand out, but nowadays there are all manner of different intepretations.

The film Love Actually captures this aspect admirably, so check it out if you want to avoid being surprised at the choice of costume/character for your child.

One rueful Mum says: ‘Gone are the days when you get a letter from the school asking you to provide a costume for your child as a shepherd/angel/wise man. They tend to include all children in a dance or at least one minute on the stage somehow so my daughter’s outfits included a soldier and a spider, and my son even featured as a robot.

‘One year the play included two little girls linking arms with the leading man and singing Diamonds Are A Girl’s Best Friend!

‘Other songs I can remember included There Must Be An Angel Playing With My Heart and Walk Like An Egyptian. The kids are either very reluctant dancers or over-enthusiastic and out of time, so the teachers at the back of the hall perform the dance actions for the kids on the stage to copy and the parents are torn between admiring Catlin being Madonna on stage, Jimmy looking like he might cry if he has to do a star jump and the teachers grooving along to the 90s music they loved at school!

‘But I’m relieved to say that at most points the play has incorporated the telling of the birth of Jesus – somehow!’ If your child has secured one of the more traditional roles and isn’t dressing up as a superhero or any other less obvious character, costumes are now available from Woolworths, who can kit out a whole production, including animals!

It’s worth noting one important tip from a Dad regarding costumes.

Obviously speaking from experience, he says: ‘Make sure your child’s is not going to be itchy on the night, otherwise you’ll have the prospect of young ladies lifting up their sheepskins to reveal rather too much of what’s underneath, or young men rummaging around under their cloaks to scratch at the places where young men always seem to scratch, irrespective of whether they have an audience or not.’ But it’s not always the children who cause amusement. As Gervase Phinn recalls in his book: ‘In one school I eavesdropped on a conversation between the headteacher and a parent concerning the nativity play the children were about to perform. “So what’s this play all about then?” asked the mother, in all seriousness.’

Top three tips from an experienced mum:

* Don’t forget your hankie (and take a tissue to hand your other half – he won’t admit it in advance but there’s bound to be the ‘ah’ factor that’ll prompt a misty-eyed response from him, too).

* Don’t shout out the lines if your child forgets them, or join in the dancing (by the time the performance is on you know their lines, and those of most of the cast, inside out) – your child will cringe with embarrassment if you try to help them out.

* Don’t use cameras or videos, even if the school still permits them. You only end up spending the whole time looking through a lens or with one hand in the air, with the result that you don’t really enjoy the performance. Some schools do their own recordings and you can buy them.