As a parent league, you have the ability to email clubs that are connected to your league.
1. Login to the league site and go to Admin > Members > Email Members.
2. Set the Report Type to Email Client Clubs.
3. The page will reload (if it does not, click Find at the bottom of the page). On the resulting page, select whether you would like to email Board Members of the connected clubs or Team Members. Then click the black arrow to open a list of Clubs connected to your league.
4. Finally, select the team positions you would like to email at the bottom of the page and click "Find Them" to generate a list of email addresses.
You can now compose your email and send to the selected users.
For steps on looking up rosters of connected clubs, refer to the help article here.