Hollywood actress Reese Witherspoon has learned the difficult aspects of raising a little boy, after her baby son DEACON asked her to explain what his penis was.

Witherspoon, who also has a six-year-old daughter called AVA with husband Ryan Phillippe, admits that 22-month-old Deacon's new vocabulary is causing the odd awkward moment.

She says, "He would say sort of, 'What's this? What's that? What's this?' So you'd say, 'That's a cup' or 'That's a microphone.'

"One day right before bed he said, 'Mama, what's this?' And I said, 'Ryan! Come up here quick!' He comes running in and he goes, 'What is it?' And I said, 'Um, I don't know, he just said, what's this.'

"He goes, 'OK, you're gonna need to leave the room.' I said, 'OK,' and so I closed the door and I twiddled my thumbs and I was biting my nails.

"He came out and he'd put him to bed and I'd said, 'What happened?' And he goes, 'I told him it was his pee-pee.' I said, 'Thank goodness, it's a pee-pee! He has a pee-pee!'

"So then the next day I come in and I go, 'Hi Deacon,' and he goes, 'Hi Mama, this is a pee-pee!' It was so cute. It's just so different having a boy from a girl."