Power tot’s terrible loneliness.

But now she has her very own "Possible Mission" – – she wants a little sister!

And Suri‘s superstar parents, Tom Cruise and Katie Holmes, can’t wait to indulge her, say pals. They’re trying for an addition to their family and hope to be successful by next year.

"’Baby sis, baby sis!’ is Suri’s new favorite phrase," a family friend told The ENQUIRER.

"Tom and Katie have been telling her for a while to expect a brother or sister…and so she keeps wondering when her ‘baby sis’ is coming. She’s not jealous – she’s anxious!"

As The ENQUIRER reported in February, Tom and Katie recently were at odds over trying for another baby right now because Katie just finished her Broadway run in All My Sons and recently began production on a new film, The Extra Man.

But the couple has decided to let nature take its course despite their work commitments, says the friend.

"They don’t want Suri to suffer from the ‘only child’ syndrome," continued the pal. "They want lots of kids, and they want her to have the joy of growing up with a sibling – especially a little sister."

For the full story and to learn the truth about Tom’s "tea parties" pick up the latest ENQUIRER – on sale now.