Brooke Mueller and Charlie Sheen

One of Charlie Sheen's newborn twin sons remains hospitalized because of low birth weight — not because of a heart condition, his rep says.

"Charlie and Brooke's infant son Max remains in the hospital, not because of a heart condition as reported, but because he has not gained the weight necessary to leave the hospital. Max is expected to reach the weight requirement shortly and will join his brother at home," Sheen's rep, Stan Rosenfield, tells People. "The Sheens appreciate the outpouring of concern, but have assured everyone that both Bob and Max are fine."

The twins were born six weeks premature on March 14, and low birth weight is common among preemies, Sheen says. The new pop also has his own theory about his son's tiny size.

"I know a lot of people are not fond of hospital food; I just didn't realize that they started so young," Sheen said.

The boys are the first children for Sheen and his wife, Brooke Mueller. Sheen has three daughters from previous relationships: Cassandra, 24, with ex-girlfriend, Paula Profit, and Sam, 5, and Lola, 3, with ex-wife Denise Richards.