"They sat with the kids by the grass beside the lake with all the public," an onlooker tells PEOPLE

By Michelle Tauber
Updated May 31, 2016 11:55 AM
Chris Jelf /Kensington Palace via Getty Image

Even future kings eat off of paper plates.

Prince William enjoyed a slice of cake off the everyday picnic staple during a family outing on May 28 to Houghton Hall International Horse Trials near their country home, Anmer Hall.

William and Princess Kate brought 1-year-old Princess Charlotte and nearly 3-year-old Prince George for the fun day out, where they also joined close friends James Meade and his wife Laura. (The Meades live nearby and James is a godfather to Charlotte.)

The royal family “were just hanging out at the horse trials with a bunch of friends,” an onlooker tells PEOPLE.

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“They sat with the kids by the grass beside the lake with all the public. They were literally just having an ordinary day out, sitting on the grass in jeans. Charlotte was running around. She’s little but she’s a good mover!”

Adds the onlooker: “The children were playing about and running around while they sat there eating cake off paper plates. William was eating cake off a paper plate just like anyone else.”

“It was just an ordinary day out with no airs and graces. But then they never do, do they? William’s just like his mum, isn’t he?

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“At some point Kate went for a little wander with the nanny and Charlotte, probably to get a bit of peace and quiet. But apart from that, they were just all hanging out in a big group.”