The royal couple pulled pints behind the bar.
The Duchess appeared utterly smitten when she met five-month-old James.
Kate Middleton opted for a classic look on her second day in Northern Ireland, pairing a bespoke Jenny Packham dress with her late mother-in-law's sapphire earrings.More news: Steelers' Brown: 'It's all about respect'
She tells Yahoo UK's 'The Royal Box': "You can imagine that every brand in the world is desperate for Meghan or Kate to be seen wearing their clothes because it's a huge endorsement, it's incredible advertising".
Barr, ever the inquisitor, then asked Kate the question on everyone's lips: "Baby number four?" She then responded, "I think William would be a little anxious".
There has been plenty of speculation as to whether the Duke and Duchess will have a fourth child, to follow in the footsteps of the Queen and Prince Philip.
William and Kate are on a two-day tour of Northern Ireland while their three children are at home in London. For the outing, which showcased Middleton's athletic side, she wore a navy quilted Barbour Longshore jacket over a white v-neck sweater with red and white stripes, black skinny jeans and navy New Balance runners.More news: Tlaib Accuses Meadows of Racism for Using Black 'Prop' to Defend Trump
It's been a busy couple of days for Kate and her other half, who stopped by Hillsborough Castle station Thursday morning to meet police officers and staff.
Overall, the Duke and Duchess have been enjoying a great time in Ireland as they received an extremely warm welcome.
They started their visit with a trip to to Windsor Park today, where they got some insight into community football projects and had a kick about.More news: Trump branded a 'conman' as ex-lawyer savages him in Congress