The reality is that juggling requires more than just the application of one's motor-skills alone. The use of other aspects of one's intelligence can be observed. Recently, I conducted a juggling class attended by a young child.
During the class, I observed that the child could toss the ball easily to a target. For this child, tossing the ball was easier than catching the ball. This is unsurprising for a child. This particular observation is not unique to young children; it can also be observed in adults.
The good news is that tossing and catching are both skills, and skills can be learned.
As I spent more time with the child doing certain juggling-related activities together, I saw how the child learned juggling (that is, the "3-Ball Cascade") through intelligent observation and comprehension of the instructions given. In my book, this child, whose motor-skills are still developing, could recognise patterns of movement, compare visual patterns in three-dimensional space, and recognise logical sequences of events.