Kate Middleton is prepping for a new royal heir!

Confirming her first pregnancy Monday, Dec. 3, the Duchess of Cambridge, 30, will be a natural mom, say pals close to Prince William**'s wife of 18 months.

"Kate will be a firm but fair mother," predicts one friend of Middleton, who will raise her baby-to-be in Apartment 1A of Kensington Palace, an upgrade from the quaint Welsh cottage where she and her husband currently call home.

Among Middleton's top parenting priorities? Keep her child grounded despite the little one's privileged upbringing. "Kate will let her children have fun and freedom, but she will also make sure they do what is best for them," a longtime pal tells Us Weekly of the pregnant royal.

The child -- boy or girl -- will jump ahead of William's kid brother, Harry, in line for the throne now that the U.K. enacted a constitutional change that gives a firstborn girl the right to succeed the throne over her younger brother. Middleton will be the first commoner in 350 years to give birth to the future king or queen of England.

Middleton and William, also 30, will take special care to surround their child with some very special commoners: Their grandparents! "William loves being at Kate's parents' house for the weekend," confirms a friend of party-supply company owners Carole and Michael, who, for all their wealth, have coal miners on their family tree. "I can imagine them spending summer visits at their grandmother and grandfather's."

And don't leave Auntie Pippa out of any playmates! "She will absolutely play a role," adds the friend. "Pippa and Kate share everything."

This article originally appeared on Usmagazine.com: Kate Middleton Will Be a "Firm But Fair" Mom, Says Pal