The actresses are both currently filming the 'Sex and the City' movie and want Cynthia's four-year-old son Charles, and Sarah's five-year-old boy James to become friends.
Cynthia - who also has an 11-year-old daughter, Samantha - said: "If we're shooting late on a Friday night, they'll come by the set.
"But James and Charlie seem to be on set different days. But we talk to Charlie about James and James about Charlie, and one day we'll figure it out so they can be there at the same time."
The flame-haired actress - who split from the children's father Danny Mozes in 2003, after falling in love with education activist Christine Marinoni - also revealed she encourages Samantha and Charles to give money to charity.