I have four boys, and struggle to get them all involved! We are starting over on a new, .25 acre property, and my (pre)teens are not at all interested. Ages 2 thru 7 always want to be put with me, but 11 hits and it's a chore.
Briana you might find this thread helpful City Kids Turned Farm Kids there are a variety of different ideas in this thread. Maybe some of the ideas could work for you.
“No hour of life is wasted that is spent in the saddle.” Winston Churchill