I’VE finally had the sex talk with my son.

With my older girls it was easy. They always asked me questions from an early age and I answered them as fully and honestly as I could. It all seemed very healthy and straightforward.

But my son is eight and was still putting his fingers in his ears and running away whenever the subject came up.

Then a few weeks ago he came home from school looking troubled and, in a slightly disgusted voice, told my new man they were going to be doing sex education at school saying, hopefully, ‘You don’t think mummy will let me do sex education do you?’ and looked downhearted when he was told ‘Oh yes, I expect she will’.

The next day he came home with a letter from school and told me he wanted me to sign the form excluding him from sex education lessons.

I can’t remember his exact phrase, but he used the word ‘inappropriate’, which just doesn’t sound right, coming from an eight-year-old.

So at bedtime I decided it was time we had a long chat and, despite him still insisting he didn’t want to know, I told him about sex.

Obviously I didn’t want to jump straight into the bodily functions stuff. But I think I may have lost his attention somewhere in my preamble.

Then there was the normal amount of giggling whenever I named body bits and eventually he seemed to take it all pretty matter-of-factly, without much comment.

Except that when I got to the end, he was still insisting he didn’t think I should be letting him do sex education in class.

Something was bothering him and it took me a while to work out exactly what it was.

Then finally all became clear when he said, ‘Yes, but what am I going to have to do in sex education?’

No wonder the poor child looked so concerned. He thought there was going to be some sort of practical element to the lesson. It made me remember a particularly funny Monty Python sketch with John Cleese playing a teacher demonstrating sex with his naked wife in front of a class full of bored teenaged boys, who are all yawning and looking out of the window and sneaking peeks at their Latin grammar books.

After I told him he wouldn’t have to DO anything, apart from try not to giggle too much, he went off to bed perfectly happily.

But the next morning I thought I’d just double check whether he now felt he understood the basic facts. He shook his head.

So we had another chat and he said, wisely I thought: “I can see I’m going to have to wear a lot of protective body armour when I’m bigger.”

And then, just to be sure he had finally understood, I told him one last time exactly which bit went in which hole and finally it seemed to dawn on him. He looked doubtful and said: “It must take a lot of complicated manoeuvres to get to that stage.”

That’s one way to put it.

But it did make me realise that he’s been playing too many war games — body armour, complicated manoeuvres — it sounded more like we’d been discussing military tactics for Call of Duty than love, sex and relationships.

My older daughters and I were trying to remember if they had had formal sex ed at primary school, and we couldn’t remember.

Maybe that’s because it wouldn’t have seemed much of a big deal to them.

I do vaguely remember a friend who had two little boys asking to go into school to see the sex ed teaching material before agreeing to her sons joining the lessons.

At the time I couldn’t really see why she was so concerned. But now, seeing the huge difference between my own three children, I do wonder if the classroom is the right place to teach young children about sex.

However carefully the lesson is handled, there is often no telling what’s going on in children’s heads. The same words can mean entirely different things to each of them, and my son certainly came home with a few very confused ideas.

IN complete contrast, it’s been my middle daughter’s 18th birthday.

She’s just finished her A-levels and is probably off to university in September.

I am immensely proud of her and will miss her like hell when she goes.

But in the meantime we had some celebrating to do.

Coming of age has more to do with getting legal ID to go out clubbing than the key to the door nowadays.

She decided it would be fun, as her birthday was a Sunday and a bit of a quiet night on the town, if she and all her friends went out in fancy dress.

The theme they hit on was cave women. Off we went to Percy’s in Newton Abbot and bought metres of fake fur.

They all came around for a barbecue and spent Sunday afternoon creating Barbarella-meets-One-Million-Years-BC cave girl outfits.

They had been upstairs for about an hour when I went to check on the progress of the costume-making. Apart from a mountain of mess on the floor, and one skirt, they weren’t getting far fast.

I remembered I’d made my oldest daughter a similar outfit four or five years ago and sure enough (she never throws anything away) we found it and used it as a prototype.

The easiest way, we discovered, was for the girls to stretch the fur around them and hold it in place, while I sewed them into the outfits.

It was working fine, they looked great. But the problem was that I was dressed in jeans and they were all skimpily dressed. The sun had graciously decided to shine and I was boiling and wanted all the windows wide open, while they insisted they were freezing.

In the end (I had had a glass of champagne with the birthday cake by then) I decided the answer was for me to strip off too and wear my other daughter’s old cave girl outfit.

I must point out the costume fitted her when she was about 15. She is only eight stone and a size eight now. And she was smaller then.

Let’s just say it’s lucky fake fur is stretchy.

Despite that, it was preposterously minuscule. It (and the champagne) made me giggle.

You must also realise I was under a certain amount of strain by that stage, given that the occasion meant spending the day with both my ex and my new partner.

It was all very grown up and civilised (well they were, I was completely juvenile), and only slightly odd now and again.

Probably the atmosphere wasn’t helped by the fact I was running around dressed in little more than fur undies.

Given that the girls’ costumes needed so little fabric, we were left with a remnant large enough to make a Fred Flintstone (possibly more Barney Rubble) style off-the-shoulder costume for my youngest son.

I wanted to get a photo of all of us together in our cavemen outfits, and so I was still wearing my disgracefully revealing, ridiculously silly outfit and making his last costume as the other partygoers arrived.

I had to breathe in a lot and probably looked a bit of an arse, but it was fun.

The girls, meanwhile, looked stunning and had a lovely (and legal) night on the town.