He thought it was where his wee went before he pee'd! I explained about his bladder but he asked me more questions.
With a secret smurk on my face I took him to dh and told him to ask daddy. So he pulls down his pj's, lifts up his willy and points at his balls, asking dh what they are called. After a very significant pause and a worried look on his face dh answers....
"Love balls"!!!!!
Can you imagine ds in the playground talking about his "love balls" FFS!!!!!