"Daddy, I used to be in mummy's tummy"
"Yes you were" I said "And guess what? I used to be in my mummy's tummy too"
"What?" she said in amazement "you were in my mummy's tummy?"
"No" I chuckled, "my mummy is your Grannie"
"Grannie is your mummy?!" she asked in disbelief.
"Daddy" she said, "after I was in mummy's tummy, I dressed as Peter Pan and then I ate all my grapes".
Ah, the last 4 years rolled into one nice easy sentence!