Apparently, it’s because of their very strict, Mary Poppins-like nanny, Maria Borrallo, who was trained at the world-famous Norland College in Bath.

Louise Heren, author of “Nanny in a Book”, outlined for The Sun what life is most likely like for the two royal children.

Rules include a firm 7 p.m. bedtime, a strict schedule that includes a lot of playtime (presumably to tire them out), limited screen time and no messing around when it comes to public engagements.

“There will be no messing,” Heren told the paper. “That’s because Maria will be aware that as they step off planes, holding mum’s hands, smiling and waving to the crowds, there can’t be any crying or terrible twos or tantrums.”

Playtimes with educational activities and games take place mostly outside Heren said, noting: “There will be lots and lots of outdoor play. … Lots of bike rides, playing with their dogs, potentially some gardening. … Yes, you are getting mucky with your hands in the soil, but you are learning how to plant.”

And even if it’s raining, George and Charlotte will still go outside.

“If it is tipping it down, they will still go out,” Heren said. “Wet weather is just inappropriate clothing, you have to put the right stuff on.”

And when it comes to mealtimes, picky eaters are not allowed, and the children are expected to try everything — as they will have to eat a variety of foods at galas when they are older.

The children are also drilled for public outings and events, and they are taught to be alert and smiling when milling with the hoi polloi.

“[Maria will] say: ‘This is your opportunity to show Mummy and Daddy just how wonderful you are, and you are to smile and be really good for them and then we can go inside and play … Maria will know their schedule. She will be doing a lot of explaining to them, what is happening,” Heren said.

And, of course, George, Charlotte (and presumably Louis) all have very strict nap times they adhere to daily.

“When you see William and Kate go off to a function and the children aren’t with them, they will be having nap time,” Heren told the Sun.