14/08/2014 16:55 BST | Updated 22/05/2015 10:12 BST

The Unexpected Things That Children Cherish

We currently going through Birthday Month – Ava was five a couple of weeks ago, Ruby will be four this weekend.

It's all very exciting (for them I mean. For me, not so much. I am literally having palpitations as I write this because of all the planning I haven't done for their joint birthday party). Yet among the frivolity, I always find myself looking back during Birthday Month, remembering the actual birth days – as well as all the birthdays the girls have had since.

Mostly, that makes me realise quite how much the girls have grown and changed (Ava is almost two-thirds my height now, which is ridiculous and, frankly, a bit disrespectful on her part, I feel). Sometimes though, it makes me realise how much they have stayed the same. You know, those little idiosyncrasies children have which must just be a part of them, rather than a fleeting, age-related whim?

You see, I've been thinking about what to get Ru for her birthday. Unlike Ava, who had ALL sorts of ideas, Ruby seems to have simpler tastes. I've got my eye on a couple of games I know she'll really enjoy – and I think she'd quite like something in the shape of a certain, very popular, chubby-cheeked, blue train.

But there's something else I could get her, which she'd probably love more than anything.

I could just get Ruby a button.

She would absolutely love a new button. The smaller the better. Shiny, probably, but not in a particularly fancy shape. Round will do just fine.

It's part of what makes Ru... Ru. When she was about 18 months old, she found a tiny red button. Not ideal, obviously (*CHOKING HAZARD*), but once she found it, wow, she loved it with all her heart.

It was a bit problematic though, if I'm honest. Ava had her own object of comfort – namely 'Pink', a shabby, completely non-pink blanket. That in itself was a bit of a pain, but at least it was large enough that we could see it from across the room. It never stayed lost for long

But Ruby's button was about the size of my little finger nail – if I didn't keep a close eye on it, it just disappeared. Ruby would ask for it in the morning, and I'd let her hold it for a bit – and then when something distracted her and she let it go, I'd (usually) put it back on the mantlepiece so we knew where to find it. As you can imagine, that plan didn't always work. The lost button days were not the happiest.

Since then, Ruby has loved a lot of buttons. There have been flower shaped ones, and pearlescent ones, and there was the one that fell of her coat, with the little fox on it.

But for want of any interesting buttons just recently, she has moved on to another object – and ever so usefully, it's even smaller than a button.

You know those rubbish toys you get in party bags, where you have to roll a little ball around until it lands in the hole (which it never does)? Two weeks ago, she managed to get one of those toys open – to free the absolutely minuscule yellow, plastic ball.

She was seriously delighted to be able to hold it in her hand. She grasped it for hours, managing to complete her every day tasks (eating, catching snails and so on), without letting it go.

When it came to pyjama time, I suggested Ruby put her ball on to the mantlepiece.

She looked at it, then at me, then at it – and very grudgingly agreed to do so.

"But, Mummy," she said, very seriously indeed, "don't touch it, k?"

I didn't touch it. I left it there. But Ruby's tall enough to reach the mantlepiece now. While that meant the tiny yellow ball enjoyed an outing to nursery the following day in Ru's pocket (and amazingly, came back again), and while it even got given a bath (without slipping down the plug hole), somewhat inevitably, the minuscule yellow ball is now missing.

It's tragic. We're still looking.

So, yes. I'm thinking I'm going to find Ruby a new button for her birthday. A tiny, shiny button that will take her mind of the missing yellow ball. And maybe also a box to put it in.

Ain't it just so lovely to be four?