The Field Hockey Canada resource centre is excellent
http://lthd.fieldhockey.ca/en/drills – comprehensive list of specific skill-based drills
http://lthd.fieldhockey.ca/en/u10lessonplans – U10 lesson plans and teaching notes
Spencer Hockey Club
http://hockey.spencerclub.org/juniors/junior_coaching_resources/ – excellent resource for drills, session plans etc.
Guildford Hockey Club
https://www.guildfordhc.com/Coaches_Area.html – useful range of junior coaching resources