As tilly pointed out, it's doable with locks, but since the semantics of locks after a fork differs from system to system, you first need to know the system before you can present a solution.

But there's a different solution. Instead of fork/exec, with the children doing the prints, open *pipes* to the children, and have the children write to the pipes. The the parent can decide in which order the results will be printed. Beware, if there's a lot of data to be printed, of which a lot is available long before the end of the life of the child, it might not work to well.

Abigail