Kathryn would make the sandwiches in the caravan kitchen, which was really a shelf and a hob in the living room – which was really a corner of the caravan with a cushion running beneath the window – but we liked it. When we arrived, Kathryn commented that the caravan was more modern than our house. ‘Look at that hob,’ she said. ‘Wipe clean. Electric. Lovely.’

‘You can’t control electric,’ I said. ‘Not like gas.’

‘And you’d know about ovens?’ she said, with half a smile.

‘I know about power supplies,’ I replied, but she was busy telling Robert not to run around the caravan.

He was exploring, which was something he liked to do – indoors. Opening cupboards, looking beneath cushions, swishing the curtains back and forth. Kathryn raised her eyebrows at me as he rushed into the toilet, looked under the seat, and made a close examination of the toilet brush. He liked to know the details of everything. ‘The toilet’s got a lock!’ he said, flipping it so the little sign went from ‘vacant’ to ‘engaged’ and back.

‘Robert, are you all right?’ Kathryn knocked softly. ‘You can come out now. We’re going in a minute.’

Moments after we’d made the sandwiches, packed the picnic bag and got our sandals on, Robert disappeared into the toilet.

‘I’m coming,’ he called, as sunny as you like, but then he stayed in there for another five minutes while we tried to remain unconcerned. I picked up the MG keys and the picnic bag. Kathryn and I stood together outside the toilet door, waiting.

‘You try him,’ she said.

‘Are you all right, son?’ I called, rapping hard on the door but trying to keep my voice light. Most likely he’d broken something in there and was trying to hide it.

‘Yes.’

‘Come on out then, will you?’

Kathryn watched me with wide eyes as I leant against the door and listened for him. ‘What’s he up to?’ she hissed.

‘Robert. We’re going to go in a minute.’

‘Coming,’ he sang out.

But the door didn’t move, and there was no sound. ‘This is why we don’t have a lock on at home,’ I said.

‘Perhaps we should just leave him. He’ll come out when he’s ready.’

‘Right, Mum, let’s go,’ I said in a loud voice, winking at Kathryn. ‘Have you got the picnic?’

Kathryn looked blank.

‘We’ll see you later, then, Robert,’ I called as I walked to the door of the caravan, opened it and closed it again, shushing Kathryn before she could say anything.

We stood in silence for a moment before she said, ‘This is silly,’ and began to bang on the toilet door with her fist. ‘Robert!’ she shouted, ‘Mummy’s worried about you! Come out now! Robert!’

He came out then, his coarse hair sticking up at the back of his head, and rushed into her arms. At that moment he looked just like her, with his big eyes and curvy lips.

‘What were you doing in there?’ I demanded.