There is no such thing as a parent or child program in Marketo. If you want to use them in SFDC, you will have to manage the things through your processes and user discipline.
if the Marketo programs are sync'ed with you child campaigns, do not change this. In SFDC, create the parents, attach the children to their parents and that's it. This means that you will have a lot of programs in Marketo, though.
If the Marketo programs are sync'ed with the parent campaigns and you want to add also leads to children (typically based on acquisition channels), do it in Marketo using the "add to SFDC campaign" flow step. Pay attention to the fact that your leads will then be members of both the parent and children campaigns in SFDC and that they will be counted twice in SFDC consolidated reporting.
The best way to set this up if you want to use the parent/child model in SFDC is :
- Stop sync'ing Marketo programs with SFDC
- Let the Parent campaigns "inactive" in SFDC (so that they do not show up in SFDC searches and in Marketo), or add some validation rules to forbid addition of members directly in Parent campaigns
- But still create 1 Marketo program for each Parent campaign, and not for children
- Sync the leads with the child campaigns only, using "add to SFDC campaign" flow steps
This is more work, but on the longer term, this is the best way to do it.