Such devoted sisters

Grace's new school year has started well. She looks relaxed and happy when I go to collect her, striding out of the classroom on long, tawny legs and flicking hair out of her eyes with the self-assurance of a sixteen-year-old. The school trip was a huge success: while I fretted and paced (and ran) she scaled tree-tops and swam lengths and filmed a bunch of lopsided, giggly dorm videos of herself and friends. The first maths classes this week have passed smoothly -- a major accomplishment for her -- and she has established a pattern of playing with two or three classmates in rotation at break, an arrangement that means she has a willing accomplice for her repeated games of Monster High every interval.

But the next hurdle has already appeared.

With Grace chatting easily beside me in the car, I park outside the home of Betty's childminder and right on cue my toddler runs outside, splendid in her pink hoody, baggy jeans and sparkly trainers. I jump out to get her. Betty pauses on the path, her dandelion white-blonde hair caught in a sudden breeze. She is scanning the car. When she spots Grace her shoulders slump.

"No Cee-Cee," Betty says, and turns back to her childminder. I scoop her up and kiss her. I tell her hello and I missed her and not to be silly. I tell her lovely Gracie has missed her too. "No Cee-Cee," she says again, but this time she sounds resigned. I take her over and open the door and put her into her car seat and buckle her in, saying brightly: "Hello Cee-Cee!" for her. Grace smiles tentatively. Betty looks at her shoes and says "Hello Cee-Cee" in a tiny voice.

Back home Grace announces that she is going to do her piano practice and disappears into the front room. Betty potters and chatters while I cook, bringing bits and pieces of coloured plastic for me to admire and occasionally giving a brisk tug on my trousers to express her impatience for food. The meal is soon ready and I ask her to go and tell Grace to come and get her tea. She won't. I ask again. She takes a few steps and then stands silently with her back to me. I ask her three times, to no response, and then tell her to please do as she is told. She runs into the front room and lets fly a barrage of angry noise, nearly-words expressing fury at Grace, who flies into the kitchen like a bat out of hell, tears streaming, to shriek at me: "I can't take any more! I'm sick of this! She hates me!"

I scold Betty, who bursts into tears and buries her face in my legs, and try to soothe Grace, who is entwined around my arm and neck, still wailing. I shuffle over to the dinner table, making soothing noises and somehow sit them both down. They are quickly distracted by the lasagne I have placed ready for them and start to eat. After a pause, Betty starts to chatter again and to try to tell me about her day. "Man," she begins. "Grandma man." She gets no further. Grace explodes into laughter and points at her, exclaiming how funny her lack of words makes her sound. Betty knits her brows and frowns deeply at Grace, hurt and cross. Grace is oblivious. She throws her head back and laughs and laughs. I ask her to be quiet and explain how Betty might be feeling as she struggles to explain herself. Betty tries again. Grace sets off laughing again. Betty is beside herself with irritation and the effort of making herself understood and starts to yell at Grace again. I count to ten in order not to raise my voice and wonder guiltily if Betty is taking her cue from me, given how often I shout at her big sister myself.

After they've eaten Grace goes off again to finish her music. As I stack the dishwasher Betty trots over to me.

"Worried," she says, and frowns again. I close the dishwasher door and click it shut and say: "Why?" "Baby," she says simply and I sit on the floor so that she can clamber into my arms and be rocked. With her head in the crook of one of my elbows and her ankles crossed in the other, she nibbles a biscuit and gazes up at me. Behind my back I can feel the warmth and hum and occasional clank of our plates being rinsed by the dishwasher. "Are you ok?" I ask Betty, and stroke her little ear. She burrows further into my arms and nibbles one of them experimentally, grazing it with her baby teeth. "Worried," she says again, conversationally. "Don't be," I tell her, "I love you." She looks up at me again, with her father's startling blue eyes, and says: "Too, Mummy."

Later, as we prepare to go upstairs for her bath, I ask her to go and say goodnight to her sister, who is watching a film. Betty runs to Grace on the sofa and kisses her with a loud smack. Grace, delighted, immediately asks her: "Do you love me Betty? Do you? Do you?"

Betty doesn't answer but runs away, casting a naughty smile over her shoulder. Grace throws a cushion after her in mock frustration. Then she turns contentedly back to the television.