The penis is too large
The Waikato Times reports that Phillip Stevens thinks the pictured genitals are too large:
His nine-year-old son had noticed the carvings as they entered the garden. “He asked us `is that a penis?’,” said Mr Stevens. “It was pretty obvious what it was, but as you go on there’s one with big testicles, then there’s one holding it. We tried not to make too big a deal of it, and just told them it was a bit inappropriate.”
He said nude works from European art traditions would not offend him in the same way as the genitalia were of more natural proportions.
So the problem is not having genitals on the carving, but that they were out of proportion!
A definite case of showing that size does matter.