Dada dumpda

In our local shopping centre, the lifts dump you right in the middle of Debenhams.
I was pushing Bella through the menswear dept. when she started gesticulating wildly and grabbing at a jumper shouting " Dada dumpda! Dada dumpda!"
She wouldn't let go and was nodding her head furiously.
This only stopped when we had payed for it and it was safely in a bag going home to Dada.
How does she know of Joe's fondness for stripy knitwear?
Then to cap it all she found a book about her and her Daddy in the library.