Each afternoon, after Betty has done her obligatory nagging for treats, and offered a few tantalising words about what she's done at school during the day, she tells me about her latest marriage proposals.
"Billy has hurt my feelings and says he wants to marry Chloe. But anyway, Jack says he will marry me now. But Lucy says she won't be my bridesmaid, because I won't play horses with her."
And: "Robert says he won't marry me now, because he hates you, because you are always buying vacuum cleaners."
(I actually think Robert has a point – the vacuum cleaner situation in our house is a bit out of control, with one residing in a corner of almost every room in the house. In fact, they are such a dominant force that poor Betty recently had a nightmare about being chased around the house by a hoover.)
Anyway Betty talks in such detail about these conversations about weddings and babies that I wonder if they ever talk about standard five-year-old stuff like their favourite sweets, or who can pick the biggest bogey.
In fact it's got to the stage where I'm growing weary of hearing about marriage, and how many babies she and her classmates plan to have between them.
But sadly, if I don't embrace the marriage talk with Betty then there would be complete silence, so I go along with it. And it seems little Jack is now the boy of the moment – in the last week, he is all Betty has talked about.
Yesterday things went onto a whole new level when Betty told me that she and Jack planned to run away to London together (that night), and live in a pink house, with an amazing garden and a huge swimming pool with loads of rubber rings in it.
The next day, armed with the perfect excuse of chatting to Jack's very cool mum and perhaps inviting her over for coffee, I cornered her in the cloakroom. Ignoring any small talk, I cut straight to the subject of our children's plans of a future in London. "Our two seem to have such a close friendship, it's just lovely," I gushed.
However, just as I was about to explore the idea of a civil ceremony for our children, she told me in no uncertain terms that Jack was very worried by Betty's constant talk of marriage. "He doesn't want to live in a house with Betty," said Jack's mum. "He just wants to stay at home with his mum and dad."
Seeing my face turn a deep shade of crimson, Betty then bellowed: "What's wrong with your face mummy?"
I leant down to Betty and, through clenched teeth, told her that when she got home that afternoon I didn't want to hear about weddings and London, I wanted to hear about reading and conkers and bogeys.
So, not only did my budding friendship with Jack's mum take a step in the wrong direction (although I am convinced we will laugh about all this in years to come, as we gaze adoringly at our grandchildren), I am left confused about what on earth has given Betty this obsession, and also paranoid about how keen she is to leave home. I thought we'd have at least a couple more years before we had to start worrying about that.