As you become older, I think it's easy to forget the constant physical contact you used to have with your siblings when you were little, and the joy and innocence of it.
I remember very well playing with my older sister, but most of the physical contact I remember was tussling (okay, fighting). I'm sure there were more tender moments of sisterly love, but hitting each other and wrestling for toys sticks more firmly in my mind!
As a mum, I enjoy seeing Ava and Ruby all jumbled up together. They think nothing of tangling their legs when they're watching a movie or falling in one big knotted heap on the trampoline.
We have even pushed their beds together in their room. Ruby kept rolling out of hers – probably, I've realised, in an attempt to make contact with her big sister. Often, when I pop my head round their door before going to bed myself, I'll see Ava sprawled out on her back, covered not with a duvet, but with a leaden, snoring Ru.
I'm sure personality comes into it. Ruby has always been a touchy-feely sort of person. When she was she really tiny, even before she could hold her own head up, she'd cling on with her legs and arms, like a little koala, when I picked her up. She's a hugger.
And Ava, who's less physical in the emotional sense, has always been okay with that.
Well, mostly. She doesn't always get it. We were in the car the other day and Ava was grasping a party bag she'd been given at school (yep, they do that in reception too when there's a birthday).
Ava had duly shared the contents, giving Ruby an annoyingly loud whistle, and two small chocolate eggs, while she opened a packet of Love Hearts and examined an impossibly tiny notepad and pencil.
With her mouth full, Ruby reached out towards Ava.
"Noo, Ru!" Ava whined. "I've shared already!"
Ruby mumbled something through the chocolate and reach further still towards her sister.
"Noo!" Ava squealed, whipping her empty (yet precious) party bag out of Ruby's grasp.
Ruby swallowed her mouthful, and then just said quietly: "Ava? Please hold my hand?"
"Oh," Ava said. And she did.
Then the other evening, I was getting the girls in their pyjamas. Ava was done and was, for some reason, lying face down on her bed with her bottom sticking in the air. Because of the angle, she had something of a builder's bum thing going on.
I was struggling to slather Ruby with her eczema emmolient, while she grappled to get on the bed with her sister.
Suddenly, Ava shrieked: "Ow! Ruby, why did you do that?"
"Sorry," Ruby replied.
The apology wasn't enough for Ava. "You PINCHED me!"
Ruby hadn't pinched Ava. I knew this because I'd seen. What she had actually done was poke her sister in the bum.
"No," Ruby said. "I didn't pinch you Ava. I did this!" Then Ruby demonstrated what she had done... by doing it again.
"Ow!" Ava squealed. "Ruby! Why did you DO that?" Her face was all scrunched up with crossness.
But it didn't stay that way for long. It unfurled into grin, and then a giggle, when Ruby replied (I believe with great honesty) "because I love you!"
MORE:Is it just me?