Jerry's mother attempts to parent her eleven-year-old son by giving him an appropriate amount of freedom and allowing him to grow, but she also wants to keep him close in order to protect him. When he tacitly expresses his desire to go to a beach that seems more "wild" than their typical spot, the narrator says,
She was thinking, Of course he's old enough to be safe without me. Have I been keeping him too close? He mustn't feel he ought to be with me. I must be careful [....]. She was determined to be neither possessive nor lacking in devotion. She went worrying off to her beach.
Even though she clearly still has concerns about his safety and his ability to make good choices, her anxiety about inadvertently making him feel obligated to her and her desire to give him enough independence overrides these concerns. Her anxiety is warranted, though, because Jerry clearly does feel a sense of obligation to her, possibly the result of his being the "man in the family" since his father has died. In considering whether to leave her alone and go off by himself, he feels "that unfailing impulse of contrition - a sort of chivalry [...], feeling it unbearable that she should go [on] by herself." Moreover, her concern about his safety and ability to make good choices is warranted as well because, one might argue, Jerry's decision to swim through the tunnel is not a sound one.
In the end, Jerry's mother seems like the typical parent: torn between giving her child the freedom she knows he needs in order to learn how to function in the world, and keeping him close in order to protect him from the world. Her parenting style reflects this internal conflict.