As thrilling as the announcement was, it threw both families into disarray. Giving Sarah and Chris their big chance meant that the parents, as well as their children, would have to relocate to Manhattan for an indefinite period. It meant that the kids would have new homes and new schools.
"I've lived in Baltimore my whole life," Sarah said. "I had everything all planned, where I was going to high school, what I was going to do next. My plans have all changed."
So Chris, Sarah and their parents have devised comforting rituals to begin each day. When David Cox drops Chris off at the rehearsal studio, father and son bump knuckles in farewell, then flutter their fingers in a manner that resembles exploding dynamite.
And just before Lisa Rosenthal leaves Sarah at the theater, she says goodbye with two lines inspired by "Project Runway." It's one of Sarah's favorite TV shows, possibly because it also features unknown artists trying to get their big break.
"Be fierce, little girl," Lisa Rosenthal tells her daughter. "Make it work."
That Sarah does.
One minute, she's sitting upstairs in the makeshift schoolroom, reading an eighth-grade biology textbook issued by the state of New York and contemplating options for a project on mitochondria. (The kids spend an average of four hours each day being tutored on the set.)
The next minute, John Mara, the "child wrangler," gets a phone call: Chris, Sarah and their understudies are needed downstairs in the rehearsal studio.
As she clambers down one flight of stairs, opens the door to the rehearsal studio and steps foot on stage, Sarah transforms herself from a confident young girl with a droll sense of humor into a frightened newcomer in a new land. Her shoulders tense and draw inward. She looks down at her feet, so that her long, brown hair partly obscures her face.
Sarah's lightning-quick metamorphosis doesn't escape actor Bobby Steggert's notice.
"Sarah has the ability to just exist on stage," he says. "She's not performing. And she seems to have learned how to do that at a very young age."
The Little Boy has more scenes and dialogue than does The Little Girl, but Sarah says that hers is the more difficult role.
"The Little Girl has to tell her story without words," Sarah says. "I have to use my movements and my emotions."
For his part, Chris possesses an analytical turn of mind that has impressed the older actors in the cast.
"To be an actor, you have to know how to be in rehearsal," says Carly Hughes, who is part of the acting ensemble and understudies the lead role of Sarah.
"The other day, the director, Marcia Milgrom Dodge, told Chris that he should be over-imploding his Ts in one scene to make sure that every consonant is audible. And Chris asked, 'Oh, and should I be doing the same thing here and here?' Not every kid would know how to take a note he had been given and apply it to other parts of his performance."
Both Chris and Sarah say that the "Ragtime" troupe has become like a family. During breaks in rehearsal, Sarah and her understudy, Kaylie Rubinaccio, 11, of Rockaway, N.J., have been weaving friendship bracelets for virtually every member of the cast and crew.
And Chris has formed a tight bond with his understudy, Ben Cook, 11, of Lorton, Va. The boys spend practically every spare minute filming videos with such titles as "Nerf Gun Zombie Attack."
If Chris and Sarah want to hold onto every moment of their time in New York - Sarah has had the silk frock she'll wear to the opening night cast party picked out for more than a month - it's partly because their time on Broadway carries a built-in expiration date.
Both are on the brink of adolescence, and both are still growing. Both have a clause in their contracts stating that if - when - their heights increase by a scant 2 inches, they will be replaced. Chris also will have to contend with a changing voice. He's a soprano now, but he won't be one forever.
"My contract is only for six months," he says. "But I want to do this for as long as I can."
When the red velvet curtain pulls back across the proscenium arch next Sunday, Kathy and David Cox, and Lisa and Ken Rosenthal will be part of an opening night audience of about 1,400. (Ken Rosenthal is a baseball reporter for FoxSports and a former columnist for The Sun.) The families went through a similar mix of terror and pride last spring when "Ragtime" opened at the Kennedy Center. But this time, the stakes will be even higher.
"As a parent, you think everything your child does is amazing," Lisa Rosenthal says. "But then she's on stage, and you're in the audience, and you're listening to people talk about her.
"And your daughter is making people cry."
Meet the Marylanders
Who: Christopher Cox
Role in Show: The Little Boy (Edgar)
Broadway Experience: Making his Broadway debut
Who: Carly Hughes
Role in Show: Ensemble; understudy for Sarah
Broadway Experience: Appeared in "The 25th Annual Putnam County Spelling Bee" and "How the Grinch Stole Christmas"
Who: Dan Manning
Hometown: Ellicott City
Role in Show: Grandfather
Broadway Experience: Making his Broadway debut
Who: Sarah Rosenthal
Role in Show: Little Girl (Tateh's Daughter)
Broadway Experience: Making her Broadway debut
Who: Bobby Steggert
Role in Show: Younger Brother
Broadway Experience: "Master Harold ... and the Boys," "110 in the Shade" and "The Slug Bearers of Kayrol Island"
If you go
"Ragtime" is in previews at the Neil Simon Theatre, 250 W. 52nd St., New York, and officially opens Nov. 15. Curtain times: 6:30 p.m. to 8 p.m. Tuesdays through Sundays, matinees 2 p.m. to 3 p.m. Wednesdays, Saturdays and Sundays. Tickets: $20-$125; premium seats $300. 212-757-8646 or neilsimontheatre.com.