redirecting output for a spawned child process..

hi... got a situation where i have a parent app that spawns children. trying to figure out how to get the output of the spawned/forked children to be written to an external file... can't seem to find any examples of how to accomplish this... do i have to insert something within the child php app itself to redirect the output that's currently being sent to the term? i'd prefer to have the output displayed, as well as redirected... these are cli apps... code chunks would be appreciated.. thanks