The note was made even more comical by the words “Fack you?” written by Belle at the top, which Willoughby assumed meant: “Thank you”.
“A story for her dad on Father’s Day,” Willoughby captioned a picture of the note, shared on Sunday 18 June.
The note reads: “Belle, once upon time there was a girl and a boy.
“Their names were Belle, Belle loves her dad. Harry was not very good at cleaning his teeth. We teach him. The end.”
Willoughby’s fans found the note hilarious and shared their own experiences of their kids writing misspelt words.
“Pmsl priceless,” one person wrote. “Frame that, it’s a ‘show the boyfriend’ thing when she’s older!”
Another wrote: “Haha I had a note from my six-year-old in his bag saying ‘F*** you mother’ - still don’t know if it was an error or a message.”
A mum also commented: “Kids are just ace. My four-year-old son gave my husband a card that said: ‘I c*** love you any more.’ They’re brilliant.”
Willoughby is also mum to seven-year-old Harry and two-year-old Chester with her husband Dan Watkins.