Just as with my unseemly (for a fortysomething father-of-two, anyway) chortling over the contents of children's books here, the amusement factor here is mainly around the inherent sniggery amusingness of the word "flaps".
It's actually the headline for this fairly grim story about the current Tongan obesity crisis, and the problem of richer countries unloading their cheap unwanted cuts of meat on poorer countries. Nonetheless you'd think they could have rustled up a female New Zealand lamb exporter to enthuse about how the Tongans love the taste of her flaps, can't get enough of her flaps, despite the unusual smell, etc. etc.
Just in case we need a bit of orientation, the BBC article includes this helpful diagram.