Plum and Bum

Yesterday we asked Lucas to pass us some grapes and plums. Lucas took me some green grapes and a big purple plum. He pointed to the plum and said 'Mamei, this is a big grape!'

Then I replied him it was actually a plum, not a grape. Then he said, 'Mamei, this is bum bum...' He was pointing to the centre line of the fruit.

I explained, 'No this is not a bum bum, this is a plum.'

And then he further commented, 'mamei, this is gu gu (a slang of penis in Cantonese).

I couldn't reply anymore......