Once, it was simple: Alfie was "my favourite little person". When we had Poppy, Alfie became "my favourite little boy". Then we had Stan, and Alfie had to become "my favourite big boy". (Today, Stan complains that he is not little at all.) So in the interest of fairness, we learn not to mention favourites.
Sometimes I tell the kids it's impossible to choose between things you love. I'm convinced this teaches them an emotional maturity rarely found in the infants. Plus, it saves hours of my thinking time every week. What's your favourite colour, Dad? I love all the colours. What's your favourite dinner, Dad? I love all food. What's your favourite song, Dad? I love all music, although please don't slip that damned Hi-5 CD in the car stereo again.
Then Poppy starts school. As a parent helper, I see her settle in at close hand. She's next door to Alfie's class, so I give cheery smiles and reassuring waves as I spy her through the window, or as she skips to assembly, even if - obedient to a fault - she dare not smile back in case that's not allowed at big school.
Before long though, this is not enough. She's sure Alfie is my favourite if I'm helping in his class and not hers. I can't fault her logic, but how can I find the time? I'm committed to my weekly appearance in Class 3. Poppy suggests helping in his class before playtime, and her class after, and Mrs Lewis agrees I might be dispensable.
So here I am, helping in Poppy's class, happy at least that I've delivered a valuable life lesson. And delivered it, no less, as a proud amateur without studying the ins and outs of child development theory.
Except when I look around there's Mrs Mills, effortlessly and skilfully dividing her attention among 30 needy reception children. No favourites. No teacher's pets. And then there's me, who can't even get my own daughter to start tile painting because she won't decide on her favourite thing at the seaside. The tile is three inches square. Fitting Poppy's choices in (the beach, the sea, having her hair "wrapped", chocolate ice cream, a boat ride) is the artistic equivalent of carving the Bible on a grain of rice.
Come on, I urge, you must have a favourite. But she is adamant. Sometimes, she tells me, you just can't choose between things you love.
Michael Cook is a freelance copywriter and a parent helper at Ernehale infants school, Arnold, Nottingham, which his children, Alfie and Poppy, attend