In an interview at the red carpet event for his new movie, Karate Kid, Jaden Smith revealed that his sister bullies him a bit, and even Jackie Chan had to agree!
This is a case where knowing the location of the planets is only half of the story. The other half of the story lies with the south node, which represents the karma, behavior patterns, and perspective of the soul as it enters this life and reveals so much more. For children, especially, south node patterns can be very pronounced and dominant because they are still 'new' on the planet and have not had enough experience on their own to grow out of these habitual behaviors that the south node reveals.
A good place to begin, though, is by looking at Mars in both children's charts, which is a planet that rules conflict, attack and defense. Because no birth times are publicly known, we can only determine the planets in the signs. Mars is in Virgo in Willow's chart, and in Cancer in Jaden's chart. While Virgo and Cancer are often agreeable signs, here they are shown to be in tension, since Willow's and Jaden's Mars placements square each other, being roughly 90 degrees apart. This points to a tendency toward heightened conflict between the siblings since their wills, Mars, are often at odds with each other.
Mars in Virgo would be more likely to be an instigator of conflict, since it can have a very critical way of expressing what it wants and what it thinks you should be doing, whereas Mars in Cancer feels more comfortable with closing down in order to protect itself and doesn't like to lash out at another. However, neither placement is particularly bullying in and of itself, even with the conflict. Two siblings may have this Mars square and fight, but who takes dominance is found elsewhere in the chart in this case.
Willow's south node is in Capricorn, which indicates that she has an angle on her personality that is focused on being able to act without being overcome with emotion or hesitation, and the desire to maintain control over herself and situations (like a general, or a manager, someone who is The Boss). This gives her a tendency to lean more toward using her will to control the behavior of others (Mars in Virgo) to get desired outcomes in the way she has planned it (Capricorn south node). Among other things, she is learning how to be more gentle and nurturing in this life with her Cancer north node.
Jaden's south node is in Pisces, which is a very gentle, soft, and kind energy but in excess has a vulnerability to letting itself be abused because it wants to approach life softly and does not like conflict or anger. Jaden comes into this life with a tendency toward passivity because of this tendency, so his Mars in Cancer is extra likely to just hunker down and go inward when conflict is initiated. Jaden's north node is in Virgo, so he's learning how to establish boundaries, to set his own rules.
Certainly if the bullying is in excess, the parents should intervene. But if it's merely because Willow has a more dominant personality, the conflict is somewhat of a grand experiment: the perfect incubator for Willow to learn more kindness and Jaden to learn more personal strength.