Charlotte sits opposite me eating a chocolate chip muffin that's almost as big as her head. She's six. There's a spray of loam-coloured crumbs fanning out from either side of her mouth and her lips are now dark brown.

We've just finished swimming. A few beads of water cling to the ends of her smoothed hair.

"That nice, Char?"

She nods slowly while staring at the chipped plastic surface of the cafe table, like she's gone into some kind of chocolate-induced trance.

It's the middle of summer. School holidays. The pool café is busy. Humid. I feel like the only Dad in existence, being surrounded by these hordes of swimsuited Mothers. Surely other Dads take their kids swimming?

I sit right up and take a good look around. A skinny blonde two tables away stares at me so sternly I slump back down. She can feck right off. Besides, her blonde twins look like clones of that kid from that creepy Poltergeist film. Should I be happy they're not like those evil twins from The Shining? Probably.

"You saving me some?" I force a smile at Char. She doesn't respond.

An older couple try squeezing between our table and the next. The woman's furry orange jacket catches our table corner and the froth spills straight off my cappuccino, right into a table pockmark. I lean forward quickly.

"Don't worry."

"Oh God, I'm so sorry," the woman apologizes, her hands fluttering. "I'm like a drunk mammoth."

"No don't worry, it's OK."

She looks at Char and chuckles. "Well, at least someone's having a nice time."

"Yeah," I smile, mopping up the froth while the pockmark, this small indenation, is making me think of craters. Surfaces.

Charlotte still seems tranced out, but now I notice her chewing has slowed right down. She's got muffin all over her front teeth.

"Hey," I wave a soggy napkin right in front of her face. "You still here?"

She looks at me. Her eyes are wide and blue and alert. She looks older. Taller.

"It's all to do with the Schrödinger equation." she says, all matter-of-fact.

I feel my eyebrows lift. "What?"

"It's derived from a first order form!"

I don't have a clue what she's on about. I feel a gentle snort flush its way down my nose. "Charlotte, what?"

She carries on chewing, swallows, and then takes another huge, messy bite of muffin. "You shouldn't worry. You're not the only Dad here," she mumbles, her mouth full. "There's one over there." She points, blatantly. She's even got a muffin smear on the end of her finger.

I look where she's pointing. She's right. There is another Dad.

She doesn't mention the Schrödinger equation or a first order form again.